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Advisory record · GHSA-mwh4-6h8g-pg8w

AIOHTTP has HTTP response splitting via \r in reason phrase

CVSS 2.7 LowEPSS 0.0030 · 23rd percentile

Published by the GitHub Advisory Database at 1 Apr 2026, 21:48 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
aiohttpPyPI<3.13.43.13.4
Identifiers
GHSA-mwh4-6h8g-pg8w · CVE-2026-34519 · PYSEC-2026-2101
Weakness (CWE)
CWE-113
Tags
Published
1 Apr 2026
Updated
10 Sept 2026

Machine-written summary

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

Summary: aiohttp versions before 3.13.4 are affected by an HTTP response splitting issue in the reason phrase of responses. An attacker can exploit this only if an application passes untrusted data into the reason parameter when creating a Response, which could let them inject extra headers or alter the response sent to clients. Upgrade to aiohttp 3.13.4 or later.

Written 5 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
2.7 Low 4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0030, the 23rd percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 1 Apr 2026, 00:00 UTC Published by the maintainers as a GitHub repository advisory
  2. 31 Oct 2026, 14:34 UTC First seen by agentprime
  3. 31 Oct 2026, 14:34 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.