Vulnerability-Lookup

CVE-2026-59903 (GCVE-0-2026-59903)

Vulnerability from cvelistv5 – Published: 2026-08-17 17:56 – Updated: 2026-08-17 18:14

Title

Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite

Summary

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, io.netty.handler.codec.http.cors.CorsHandler setVaryHeader replaces application Vary headers such as Authorization or Cookie with Origin, allowing a caching proxy or CDN to reuse authenticated responses across users and disclose sensitive information. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Severity

6.5 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-17 18:13 UTC

CWE

CWE-524 - Use of Cache Containing Sensitive Information

Assigner

GitHub_M

References

5 references

URL	Tags
https://github.com/netty/netty/security/advisorie…	x_refsource_CONFIRM
https://github.com/netty/netty/pull/17213	x_refsource_MISC
https://github.com/netty/netty/pull/17217	x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty…	x_refsource_MISC
https://github.com/netty/netty/releases/tag/netty…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
netty	netty	Affected: < 4.1.137.Final Affected: >= 4.2.0.Final, < 4.2.17.Final	guessed

Show details on NVD website

JSON

To clipboard

{
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                "id": "CVE-2026-59903",
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        }
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      "metrics": [
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            "confidentialityImpact": "HIGH",
            "integrityImpact": "LOW",
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      "source": {
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      "title": "Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite"
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    "dateReserved": "2026-07-07T16:40:07.984Z",
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FKIE_CVE-2026-59903

Vulnerability from fkie_nvd - Published: 2026-08-17 18:17 - Updated: 2026-08-17 19:16

Severity

6.5 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/netty/netty/pull/17213
	security-advisories@github.com	https://github.com/netty/netty/pull/17217
	security-advisories@github.com	https://github.com/netty/netty/releases/tag/netty-4.1.137.Final
	security-advisories@github.com	https://github.com/netty/netty/releases/tag/netty-4.2.17.Final
	security-advisories@github.com	https://github.com/netty/netty/security/advisories/GHSA-8c42-7qj2-3j46

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "netty",
          "vendor": "netty",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 4.1.137.Final"
            },
            {
              "status": "affected",
              "version": "\u003e= 4.2.0.Final, \u003c 4.2.17.Final"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, io.netty.handler.codec.http.cors.CorsHandler setVaryHeader replaces application Vary headers such as Authorization or Cookie with Origin, allowing a caching proxy or CDN to reuse authenticated responses across users and disclose sensitive information. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final."
    }
  ],
  "id": "CVE-2026-59903",
  "lastModified": "2026-08-17T19:16:32.890",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 4.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
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    },
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      "source": "security-advisories@github.com",
      "url": "https://github.com/netty/netty/pull/17217"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/netty/netty/releases/tag/netty-4.1.137.Final"
    },
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      "url": "https://github.com/netty/netty/releases/tag/netty-4.2.17.Final"
    },
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    }
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GHSA-8C42-7QJ2-3J46

Vulnerability from github – Published: 2026-08-17 18:24 – Updated: 2026-08-17 18:24

Summary

Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite

Details

Summary

Netty's CorsHandler silently overwrites existing Vary headers, enabling cache poisoning and sensitive information disclosure.

Details

io.netty.handler.codec.http.cors.CorsHandler#setVaryHeader overwrites any existing Vary headers set by backend applications.

    private static void setVaryHeader(final HttpResponse response) {
        response.headers().set(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN);
    }

Because set() replaces all existing values for the header, if a backend application sets a Vary header (such as Vary: Authorization or Vary: Cookie) to ensure that intermediate caches (like CDNs) cache responses separately per user, the CorsHandler will overwrite it with Vary: origin. This causes the caching proxy to ignore the authorization context and cache the response based solely on the URL and Origin, allowing an attacker to retrieve another user's cached sensitive data.

Impact

This is a Cache Poisoning vulnerability that leads to Information Disclosure. It impacts any Netty-based web application that uses the CorsHandler, sets its own Vary headers to manage caching of authenticated or user-specific responses (e.g., Vary: Authorization), and is deployed behind a caching proxy or CDN. The end-users of these applications are impacted, as their sensitive data may be leaked to unauthorized actors.

Severity

6.5 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.2.16.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-codec-http"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.2.0.Final"
            },
            {
              "fixed": "4.2.17.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.136.Final"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "io.netty:netty-codec-http"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.1.137.Final"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59903"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-524"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-17T18:24:26Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\nNetty\u0027s `CorsHandler` silently overwrites existing `Vary` headers, enabling cache poisoning and sensitive information disclosure.\n\n### Details\n`io.netty.handler.codec.http.cors.CorsHandler#setVaryHeader` overwrites any existing Vary headers set by backend applications. \n\n```java\n    private static void setVaryHeader(final HttpResponse response) {\n        response.headers().set(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN);\n    }\n```\n\nBecause `set()` replaces all existing values for the header, if a backend application sets a `Vary` header (such as `Vary: Authorization` or `Vary: Cookie`) to ensure that intermediate caches (like CDNs) cache responses separately per user, the `CorsHandler` will overwrite it with `Vary: origin`. This causes the caching proxy to ignore the authorization context and cache the response based solely on the URL and Origin, allowing an attacker to retrieve another user\u0027s cached sensitive data.\n\n### Impact\nThis is a Cache Poisoning vulnerability that leads to Information Disclosure. It impacts any Netty-based web application that uses the CorsHandler, sets its own Vary headers to manage caching of authenticated or user-specific responses (e.g., Vary: Authorization), and is deployed behind a caching proxy or CDN. The end-users of these applications are impacted, as their sensitive data may be leaked to unauthorized actors.",
  "id": "GHSA-8c42-7qj2-3j46",
  "modified": "2026-08-17T18:24:26Z",
  "published": "2026-08-17T18:24:26Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/security/advisories/GHSA-8c42-7qj2-3j46"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/pull/17213"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/pull/17217"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/netty/netty"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/releases/tag/netty-4.1.137.Final"
    },
    {
      "type": "WEB",
      "url": "https://github.com/netty/netty/releases/tag/netty-4.2.17.Final"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite"
}

Sightings

Author	Source	Type	Date	Other

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-59903 (GCVE-0-2026-59903)

FKIE_CVE-2026-59903

GHSA-8C42-7QJ2-3J46

Summary

Details

Impact

Tags

Sightings

Nomenclature