CVE-2026-34520

EUVD-2026-18046
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.
HTTP Request/Response Splitting
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
9.1 CRITICAL
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Base Score
CVSS 3.x
EPSS Score
Percentile: 19%
Affected Products (NVD)
VendorProductVersion
aiohttpaiohttp
𝑥
< 3.13.4
𝑥
= Vulnerable software versions
Common Weakness Enumeration
References
https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf