CVE-2026-34520

CRITICAL9.1

AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass

Published Apr 1, 2026

Modified 3 weeks ago

Details

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.

References

WEB

https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4

WEB

https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4

WEB

https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf

ADVISORY

https://www.cve.org/CVERecord?id=CVE-2026-34520

CVSS Analysis

CVSS v4.0

2.7