CVE-2026-34520AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass

Description

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf PatchVendor Advisory
• https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4 Patch
• https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 Release Notes