CVE-2026-75595 netty CVE debrief

Who should care

Defenders responsible for Netty deployments, particularly those using per-SNI clientAuth=REQUIRE as the sole mutual TLS gate, should assess the exposure of their systems and prioritize updating to patched versions.

Why it matters

CVE-2026-75595 is a critical vulnerability in the Netty framework that allows an unauthenticated remote attacker to bypass mutual TLS requirements under certain conditions. Defenders responsible for Netty deployments should assess the exposure of their systems and prioritize updating to patched versions.

• Unauthenticated remote attackers can bypass mutual TLS requirements.
• Defenders need to verify that their deployments use per-SNI clientAuth=REQUIRE as the sole mutual TLS gate.
• Updating to patched versions of Netty is a high priority.

Technical summary

The SslClientHelloHandler class in Netty incorrectly handles TLS handshake headers, allowing an unauthenticated remote attacker to bypass mutual TLS requirements. The vulnerability affects Netty versions prior to 4.1.137.Final and 4.2.17.Final. This issue arises from the incorrect offset check before reading the four-byte TLS handshake header, which can lead to an IndexOutOfBoundsException. Consequently, the default SslContext may be selected instead of the SNI-specific context, potentially bypassing mutual TLS requirements in certain deployments.

Defensive priority

High priority should be given to updating Netty to versions 4.1.137.Final or 4.2.17.Final, or later, as these versions include patches for the vulnerability. Additionally, defenders should verify that their deployments use per-SNI clientAuth=REQUIRE as the sole mutual TLS gate and assess the exposure of their systems.

Recommended defensive actions

• Update Netty to version 4.1.137.Final or 4.2.17.Final, or later.
• Verify that deployments use per-SNI clientAuth=REQUIRE as the sole mutual TLS gate.
• Assess the exposure of systems using affected versions of Netty.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record and NVD vulnerability detail provide information on the vulnerability, its impact, and the affected versions of Netty. The source references include patches, issue tracking, and release notes from the Netty project.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.