CVE-2026-44249: Netty handler Netty Has An IPv6 Subnet Vulnerability

HIGH
Advisory Identifier: GHSA-3qp7-7mw8-wx86
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CVSS 8.1
CWE-284 CWE-697
Published
Advisory Summary

CVE-2026-44249 is a HIGH (CVSS 8.1) netty has an ipv6 subnet vulnerability (CWE-284: Improper Access Control) affecting Netty handler libraries in the Maven ecosystem. The issue involves netty has an ipv6 subnet filter bypass via incorrect comparator masking. Remediation is available by upgrading affected packages to version 4.2.15.Final, 4.1.135.Final.

CVE-2026-44249 at a Glance

CVE Identifier CVE-2026-44249
GHSA Identifier GHSA-3qp7-7mw8-wx86
Severity HIGH
CVSS v3.1 Base Score 8.1
CWE Classification CWE-284: Improper Access Control
Affected Product Netty handler
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 8.1

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:H/A:H).

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 High (I:H)
Availability High (A:H)

How to Fix CVE-2026-44249

To remediate this vulnerability, upgrade all affected Netty handler 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-handler fixed: 4.2.15.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-handler</artifactId>
    <version>4.2.15.Final</version>
</dependency>
io.netty:netty-handler fixed: 4.1.135.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-handler</artifactId>
    <version>4.1.135.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-2026-44249, 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 handler in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.15.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-284: Improper Access Control, where the product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. In Netty handler, 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 An attacker can bypass IPv6 subnet rules due to an incorrect masking operation in IpSubnetFilterRule.compareTo(). Valid public IP addresses can bypass the restrictions. ### Details `io.netty.handler.ipfilter.IpSubnetFilterRule#compareTo(java.net.InetSocketAddress)` method performs a bitwise AND between the incoming IP address and the configured networkAddress, instead of the subnetMask. ### Impact Access Control Bypass. Attacker can bypass IpSubnetFilter IPv6 access controls.

CVE-2026-44249 Affected Netty handler Versions

2 component(s)
Fixed Versions:
4.2.15.Final4.1.135.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-handler
maven/io.netty/netty-handler
Maven
≥ 4.2.0.Final
< 4.2.15.Final
4.2.15.Final
io.netty:netty-handler
maven/io.netty/netty-handler
Maven
< 4.1.135.Final
4.1.135.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-3qp7-7mw8-wx86
NVD — CVE-2026-44249 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-44249
Netty handler Source Repository REPOSITORY
https://github.com/netty/netty
Netty handler Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.1.135.Final
Netty handler Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.15.Final

Frequently Asked Questions

What is CVE-2026-44249?
CVE-2026-44249 is a security vulnerability in Netty handler involving Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking under CWE-284: Improper Access Control.
Which Netty handler versions are affected?
Affected versions include releases prior to 4.2.15.Final, 4.1.135.Final across affected packages: io.netty:netty-handler.
What version fixes CVE-2026-44249?
Upgrading to 4.2.15.Final, 4.1.135.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-handler affected?
Yes, io.netty:netty-handler is affected in releases prior to 4.2.15.Final, 4.1.135.Final. Upgrade your dependency to 4.2.15.Final, 4.1.135.Final or later.
What is the CVSS score of CVE-2026-44249?
CVE-2026-44249 has a CVSS v3.1 base score of 8.1 (HIGH) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-44249?
CVE-2026-44249 is classified under CWE-284: Improper Access Control (The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.).
How can I check Maven dependencies for CVE-2026-44249?
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-3qp7-7mw8-wx86",
  "modified" : "2026-06-12T19:27:07Z",
  "published" : "2026-06-08T19:00:33Z",
  "aliases" : [ "CVE-2026-44249" ],
  "summary" : "Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking",
  "details" : "### Summary\nAn attacker can bypass IPv6 subnet rules due to an incorrect masking operation in IpSubnetFilterRule.compareTo(). Valid public IP addresses can bypass the restrictions.\n\n### Details\n`io.netty.handler.ipfilter.IpSubnetFilterRule#compareTo(java.net.InetSocketAddress)` method performs a bitwise AND between the incoming IP address and the configured networkAddress, instead of the subnetMask.\n\n### Impact\nAccess Control Bypass. Attacker can bypass IpSubnetFilter IPv6 access controls.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-handler"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.15.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.14.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-handler"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.135.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.134.Final"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-3qp7-7mw8-wx86"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44249"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.1.135.Final"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.15.Final"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-284", "CWE-697" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-08T19:00:33Z",
    "nvd_published_at" : "2026-06-11T22:16:56Z"
  }
}