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PYSEC-2026-1104

AIOHTTP is vulnerable to HTTP Request/Response Smuggling through incorrect parsing of chunked trailer sections

Quick fix

PYSEC-2026-1104 — aiohttp: upgrade to the fixed version with the command below.

pip install --upgrade 'aiohttp>=3.12.14'

Details

### Summary The Python parser is vulnerable to a request smuggling vulnerability due to not parsing trailer sections of an HTTP request.

### Impact If a pure Python version of aiohttp is installed (i.e. without the usual C extensions) or AIOHTTP_NO_EXTENSIONS is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections.

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Patch: https://github.com/aio-libs/aiohttp/commit/e8d774f635dc6d1cd3174d0e38891da5de0e2b6a

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI/aiohttp

Introduced in: 0Fixed in: 3.12.14

Fixpip install --upgrade 'aiohttp>=3.12.14'

References

https://github.com/aio-libs/aiohttp/security/advisories/GHSA-9548-qrrj-x5pj[WEB]
https://nvd.nist.gov/vuln/detail/CVE-2025-53643[ADVISORY]
https://github.com/aio-libs/aiohttp/commit/e8d774f635dc6d1cd3174d0e38891da5de0e2b6a[FIX]
https://github.com/aio-libs/aiohttp[PACKAGE]
https://pypi.org/project/aiohttp[PACKAGE]
https://github.com/advisories/GHSA-9548-qrrj-x5pj[ADVISORY]