How severe is CVE-2026-44249?

CVE-2026-44249 has a CVSS score of 8.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-44249?

CVE-2026-44249 affects the following packages: io.netty:netty-handler (Maven), io.netty:netty-handler (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-44249?

Update io.netty:netty-handler to 4.2.15.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44249 is resolved across your whole dependency graph.

How do I detect CVE-2026-44249 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-handler, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-44249 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-44249 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-44249 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-44249?

CVE-2026-44249 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 69th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-44249?

CVE-2026-44249 is classified as CWE-284 (CWE-284), CWE-697 (CWE-697), CWE-1287 (CWE-1287). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-44249 published, and has it been updated?

CVE-2026-44249 was published on June 11, 2026 and was last updated on September 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

HIGH severity

CVE-2026-44249 — netty-handler

HIGH

CVE-2026-44249 is a high-severity (CVSS 8.1) CWE-284 vulnerability in io.netty:netty-handler. A fix is available for io.netty:netty-handler — see the affected versions and patch details below.

Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking

Also known asGHSA-3qp7-7mw8-wx86

Published

Jun 11, 2026

Updated

Sep 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Sep 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44249.

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs69th percentile — riskier than 69% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-44249 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

☕io.netty:netty-handler☕io.netty:netty-handler

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`io.netty:netty-handler`	≥ 4.2.0.Final&&< 4.2.15.Final	4.2.15.Final`io.netty:netty-handler:4.2.15.Final`
☕Maven	`io.netty:netty-handler`	all versions	4.1.135.Final`io.netty:netty-handler:4.1.135.Final`

Affected Products

1 product · 2 configurations

Application

nettynetty

≥ 4.2.0 && < 4.2.15

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-handler, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-handler to 4.2.15.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44249 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This vulnerability in netty-handler is rated as Important because a remote attacker can bypass configured IPv6 subnet filtering rules. This flaw, stemming from an incorrect masking operation, could allow unauthorized access to or exposure of services that are intended to be network-restricted within Red Hat products…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-44249 (CC BY 4.0)

Product	Fixed in	Advisory
AMQ Clients 2026.Q3	`netty-handler`	RHSA-2026:69459
Cryostat 4 on RHEL 9	`cryostat/cryostat-reports-rhel9:4.2.0-13`	RHSA-2026:48151
Red Hat AMQ Broker 7.13.6	`netty-handler`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`netty-handler`	RHSA-2026:66488
Red Hat Build of Apache Camel 3.33 for Quarkus 3.33.2.SP1	`netty-handler`	RHSA-2026:26586
Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16	`netty-handler`	RHSA-2026:37390
Red Hat build of Quarkus 3.27.4.SP1	`netty-handler`	RHSA-2026:26018
Red Hat build of Quarkus 3.33.2.SP1	`netty-handler`	RHSA-2026:26017

Frequently Asked Questions

### 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.

O3 Security · Impact-Aware SCA

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