CVE-2026-59903: Netty codec http Netty Vulnerable To Cache Poisoning Vulnerability

MODERATE
Advisory Identifier: GHSA-8c42-7qj2-3j46
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CVSS 6.5
CWE-524
Published
Advisory Summary

CVE-2026-59903 is a MODERATE (CVSS 6.5) netty vulnerable to cache poisoning vulnerability (CWE-524: Use of Cache Containing Sensitive Information) affecting Netty codec http libraries in the Maven ecosystem. The issue involves netty vulnerable to cache poisoning and information disclosure via cors vary header overwrite. Remediation is available by upgrading affected packages to version 4.2.17.Final, 4.1.137.Final.

CVE-2026-59903 at a Glance

CVE Identifier CVE-2026-59903
GHSA Identifier GHSA-8c42-7qj2-3j46
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-524: Use of Cache Containing Sensitive Information
Affected Product Netty codec http
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-59903

To remediate this vulnerability, upgrade all affected Netty codec http dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

io.netty:netty-codec-http fixed: 4.2.17.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.2.17.Final</version>
</dependency>
io.netty:netty-codec-http fixed: 4.1.137.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.1.137.Final</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=io.netty

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-59903, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=io.netty

Analyze the terminal output to locate any version of Netty codec http in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.17.Final), your application is affected.

Note: The mvn dependency:tree -Dincludes=io.netty command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-524: Use of Cache Containing Sensitive Information, where the code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. In Netty codec http, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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. ```java 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.

CVE-2026-59903 Affected Netty codec http Versions

2 component(s)
Fixed Versions:
4.2.17.Final4.1.137.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
≥ 4.2.0.Final
< 4.2.17.Final
4.2.17.Final
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
< 4.1.137.Final
4.1.137.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-8c42-7qj2-3j46
Netty codec http Source Repository REPOSITORY
https://github.com/netty/netty/pull/17213
Netty codec http Source Repository REPOSITORY
https://github.com/netty/netty/pull/17217
Netty codec http Source Repository REPOSITORY
https://github.com/netty/netty
Netty codec http Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.1.137.Final
Netty codec http Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.17.Final

Frequently Asked Questions

What is CVE-2026-59903?
CVE-2026-59903 is a security vulnerability in Netty codec http involving Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite under CWE-524: Use of Cache Containing Sensitive Information.
Which Netty codec http versions are affected?
Affected versions include releases prior to 4.2.17.Final, 4.1.137.Final across affected packages: io.netty:netty-codec-http.
What version fixes CVE-2026-59903?
Upgrading to 4.2.17.Final, 4.1.137.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-codec-http affected?
Yes, io.netty:netty-codec-http is affected in releases prior to 4.2.17.Final, 4.1.137.Final. Upgrade your dependency to 4.2.17.Final, 4.1.137.Final or later.
What is the CVSS score of CVE-2026-59903?
CVE-2026-59903 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N.
What CWE is associated with CVE-2026-59903?
CVE-2026-59903 is classified under CWE-524: Use of Cache Containing Sensitive Information (The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere.).
How can I check Maven dependencies for CVE-2026-59903?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=io.netty'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8c42-7qj2-3j46",
  "modified" : "2026-08-17T18:24:26Z",
  "published" : "2026-08-17T18:24:26Z",
  "aliases" : [ "CVE-2026-59903" ],
  "summary" : "Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite",
  "details" : "### Summary\nNetty's `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's 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.17.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.16.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.137.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.136.Final"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-524" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-17T18:24:26Z",
    "nvd_published_at" : null
  }
}