# CVE-2026-44249: Netty IPv6 subnet filter bypass in netty-handler

Source: https://junglewise.ai/threats/cve-2026-44249-netty-ipv6-subnet-filter-bypass-in-netty-handler  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-11. Updated: 2026-06-11  
License: CC BY 4.0 with a link back

CVE-2026-44249 · Severity: high · CVSS 8.1 · Published 2026-06-11

Netty is a widely used networking framework that helps developers build high-performance servers and clients. A flaw in its IP filtering component allows attackers to bypass security rules designed to restrict access based on IPv6 addresses. This could allow unauthorized users to connect to sensitive services or bypass network-level protections, potentially leading to unauthorized data access or service disruption.

Technologies: [io.netty:netty-handler (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-handler). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven).

## Quick answers

**Is CVE-2026-44249 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-44249 being exploited in the wild.

**How severe is CVE-2026-44249?** High severity, with a CVSS score of 8.1, published 11 June 2026.

**Which products and versions are affected?** io.netty:netty-handler (Maven) ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.15.Final.

**Is there a fix for CVE-2026-44249?** Yes. io.netty:netty-handler (Maven): upgrade to 4.2.15.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-44249 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-44249?** Check whether you run io.netty:netty-handler (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-handler (Maven): upgrade to 4.2.15.Final or later

  ```sh
  # set io.netty:netty-handler to 4.2.15.Final in your pom.xml or build.gradle
  ```


## Technical details

An access control bypass vulnerability exists in the netty-handler component of the Netty framework. The root cause is an incorrect bitwise masking operation within the IpSubnetFilterRule.compareTo() method, where the incoming IP address is incorrectly compared against the networkAddress instead of the subnetMask. This logic error allows valid public IPv6 addresses to bypass configured subnet restrictions. The attack is network-reachable and requires no privileges or user interaction, though it is rated with high complexity as it depends on specific IPv6 address configurations. The issue is resolved in versions 4.1.135.Final and 4.2.15.Final.

## Affected products

- Netty Project Netty < 4.1.135.Final, >= 4.2.0.Final, <= 4.2.14.Final

## Identifiers

- CVE-2026-44249
- GHSA-3qp7-7mw8-wx86

## Timeline

- 2026-06-02: patched: Versions 4.1.135.Final and 4.2.15.Final released
- 2026-06-05: advisory: GitHub Security Advisory GHSA-3qp7-7mw8-wx86 published
- 2026-06-11: disclosed: CVE-2026-44249 published to NVD

## References

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

## Related threats

- [Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.](https://junglewise.ai/threats/cve-2026-75596-netty-quadratic-pre-handshake-clienthello-reassembly-in-sni)
- [Netty SNI routing bypass via fragmented TLS ClientHello](https://junglewise.ai/threats/cve-2026-75595-netty-sni-routing-bypass-via-fragmented-tls-clienthello)
- [Netty disabled TLS hostname verification in netty-handler](https://junglewise.ai/threats/cve-2026-50010-netty-disabled-tls-hostname-verification-in-netty-handler)
- [Netty excessive memory allocation in SNIHandler](https://junglewise.ai/threats/cve-2026-45416-netty-excessive-memory-allocation-in-snihandler)
- [SslHandler doesn't correctly validate packets which can lead to native crash when using native SSLEngine](https://junglewise.ai/threats/cve-2025-24970-sslhandler-doesn-t-correctly-validate-packets-which-can-lead-to)