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Advisory record · GHSA-c4c3-7fpv-j4q5

Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext

CVSS 9.1 CriticalCriticalEPSS 0.0032 · 24th percentile

Critical, because:

  • CVSS score 9.1: 9.0 or more.

How we decide what’s critical

Published by the GitHub Advisory Database at 8 Sept 2026, 18:16 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
io.netty:netty-handlerMaven>=4.2.0.Final, <4.2.17.Final || <4.1.137.Final4.2.17.Final, 4.1.137.Final
Identifiers
GHSA-c4c3-7fpv-j4q5 · CVE-2026-75595
Weakness (CWE)
CWE-475 · CWE-754
Tags
Published
8 Sept 2026
Updated
8 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Netty's io.netty:netty-handler is affected in versions from 4.2.0.Final before 4.2.17.Final and from 4.1.x before 4.1.137.Final. A remote, unauthenticated attacker can send a TLS ClientHello split across records so that Netty falls back to the default SslContext instead of the per-SNI one. This bypasses mTLS only when the default context does not require client authentication and no other peer-certificate check exists. Upgrade to 4.2.17.Final or 4.1.137.Final.

Written 2 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
9.1 Critical 4.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0032, the 24th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:18 UTC First seen by agentprime
  2. 31 Oct 2026, 14:18 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.