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Advisory record · GHSA-f256-j965-7f32

Possible request smuggling in HTTP/2 due missing validation of content-length

CVSS 5.9 MediumEPSS 0.049 · 92nd percentile

Published by the GitHub Advisory Database at 30 Mar 2021, 15:10 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
io.netty:netty-codec-http2Maven>=4.0.0, <4.1.61.Final4.1.61.Final
org.jboss.netty:nettyMavenall versionsNo fixed version yet
io.netty:nettyMavenall versionsNo fixed version yet
Identifiers
GHSA-f256-j965-7f32 · CVE-2021-21409
Weakness (CWE)
CWE-444
Tags
Published
30 Mar 2021
Updated
10 Sept 2026

Machine-written summary

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

The io.netty:netty-codec-http2 package versions from 4.0.0 before 4.1.61.Final are affected. The content-length header is not validated when a request consists of a single HTTP/2 headers frame with end-of-stream set, so an attacker can smuggle requests if a proxy forwards that request to a peer as HTTP/1.1. Upgrade to 4.1.61.Final or later; alternatively, validate the content-length header before proxying requests.

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
5.9 Medium 3.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.049, the 92nd 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.