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Advisory record · GHSA-c427-h43c-vf67

AIOHTTP accepts duplicate Host headers

CVSS 6.3 MediumEPSS 0.0030 · 22nd percentile

Published by the GitHub Advisory Database at 1 Apr 2026, 21:49 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-c427-h43c-vf67 · CVE-2026-34525 · PYSEC-2026-2103
Weakness (CWE)
CWE-20 · CWE-444
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.

AIOHTTP (aiohttp) versions before 3.13.4 accept requests with multiple Host headers. The source says this mainly matters when a reverse proxy applies security rules based on the Host header, since the proxy and aiohttp could then interpret different host names and a request might reach a privileged sub app set up with Application.add_domain(). Upgrade to aiohttp 3.13.4 or later.

Written 1 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
6.3 Medium 4.0 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0030, the 22nd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:11 UTC First seen by agentprime
  2. 31 Oct 2026, 14:11 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.