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Advisory record · GHSA-fccg-mwvh-qqg4

Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing

CVSS 8.7 HighEPSS 0.0037 · 31st percentile

Published by the GitHub Advisory Database at 8 Sept 2026, 18:14 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-fccg-mwvh-qqg4 · CVE-2026-75596
Weakness (CWE)
CWE-407
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 io.netty:netty-handler versions 4.2.0.Final up to 4.2.17.Final and 4.1.x before 4.1.137.Final are affected. A remote, unauthenticated attacker can send a ClientHello split into many tiny TLS records before the handshake completes, causing quadratic CPU work on the event loop and degrading TLS connection handling for other clients. 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
8.7 High 4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0037, the 31st percentile, on 7 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.