CVE-2026-34525

AIOHTTP: Duplicate Host header accepted

CVSS 6.3 MEDIUMEPSS 0.3%CWE-20 CWE-444

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 6.3EPSS 0.3%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

01 Apr 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, multiple Host headers were allowed in aiohttp. This issue has been patched in version 3.13.4.

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

Affected products

aio-libs · aiohttp

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References

https://github.com/aio-libs/aiohttp/commit/53e2e6fc58b89c6185be7820bd2c9f40216b3000 https://github.com/aio-libs/aiohttp/commit/e00ca3cca92c465c7913c4beb763a72da9ed8349 https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 https://github.com/aio-libs/aiohttp/security/advisories/GHSA-c427-h43c-vf67