CVE-2026-56817: Netty XML Injection / Risky Sink — Vulnerability

HIGH
Advisory Identifier: GHSA-4qhr-g3c6-fcfx
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CWE-611
Published
Advisory Summary

CVE-2026-56817 is a HIGH injection / risky sink — vulnerability (CWE-611: Improper Restriction of XML External Entity Reference) affecting Netty XML libraries in the Maven ecosystem. The issue involves injection / risky sink — unconfigured xml factory with active dtd and entity handling. Remediation is available by upgrading affected packages to version 4.2.16.Final, 4.1.136.Final.

CVE-2026-56817 at a Glance

CVE Identifier CVE-2026-56817
GHSA Identifier GHSA-4qhr-g3c6-fcfx
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-611: Improper Restriction of XML External Entity Reference
Affected Product Netty XML
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-56817

To remediate this vulnerability, upgrade all affected Netty XML 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-xml fixed: 4.2.16.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-xml</artifactId>
    <version>4.2.16.Final</version>
</dependency>
io.netty:netty-codec-xml fixed: 4.1.136.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-xml</artifactId>
    <version>4.1.136.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-2026-56817, 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 XML in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.16.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-611: Improper Restriction of XML External Entity Reference, where the product processes an xml document that can contain xml entities with uris that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. In Netty XML, 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

Any caller that can deliver bytes to a Netty channel pipeline containing `XmlDecoder` can send XML with a DOCTYPE declaration to a parser instantiated with no security configuration — but whether external entities are actually resolved depends on Aalto XML's async parser behavior, making this a confirmed misconfiguration with conditional exploitability.

CVE-2026-56817 Affected Netty XML Versions

2 component(s)
Fixed Versions:
4.2.16.Final4.1.136.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-codec-xml
maven/io.netty/netty-codec-xml
Maven
≥ 4.2.0.Final
< 4.2.16.Final
4.2.16.Final
io.netty:netty-codec-xml
maven/io.netty/netty-codec-xml
Maven
≥ 4.1.0.Final
< 4.1.136.Final
4.1.136.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-4qhr-g3c6-fcfx
NVD — CVE-2026-56817 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-56817
Security Fix Commit FIX COMMIT
https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
Security Fix Commit FIX COMMIT
https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6
Netty XML Source Repository REPOSITORY
https://github.com/netty/netty
Netty XML Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
Netty XML Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final

Frequently Asked Questions

What is CVE-2026-56817?
CVE-2026-56817 is a security vulnerability in Netty XML involving Injection / Risky Sink — unconfigured XML factory with active DTD and entity handling under CWE-611: Improper Restriction of XML External Entity Reference.
Which Netty XML versions are affected?
Affected versions include releases prior to 4.2.16.Final, 4.1.136.Final across affected packages: io.netty:netty-codec-xml.
What version fixes CVE-2026-56817?
Upgrading to 4.2.16.Final, 4.1.136.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-codec-xml affected?
Yes, io.netty:netty-codec-xml is affected in releases prior to 4.2.16.Final, 4.1.136.Final. Upgrade your dependency to 4.2.16.Final, 4.1.136.Final or later.
What CWE is associated with CVE-2026-56817?
CVE-2026-56817 is classified under CWE-611: Improper Restriction of XML External Entity Reference (The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.).
How can I check Maven dependencies for CVE-2026-56817?
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-4qhr-g3c6-fcfx",
  "modified" : "2026-07-22T21:43:17Z",
  "published" : "2026-07-22T21:43:16Z",
  "aliases" : [ "CVE-2026-56817" ],
  "summary" : "Netty XML: Injection / Risky Sink — unconfigured XML factory with active DTD and entity handling",
  "details" : "Any caller that can deliver bytes to a Netty channel pipeline containing `XmlDecoder` can send XML with a DOCTYPE declaration to a parser instantiated with no security configuration — but whether external entities are actually resolved depends on Aalto XML's async parser behavior, making this a confirmed misconfiguration with conditional exploitability.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-xml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.16.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.15.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-xml"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.0.Final"
      }, {
        "fixed" : "4.1.136.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.135.Final"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-4qhr-g3c6-fcfx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-56817"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.1.136.Final"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.16.Final"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-611" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-22T21:43:16Z",
    "nvd_published_at" : "2026-07-21T23:17:52Z"
  }
}