CVE-2026-34520
CRITICALAIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
Title source: cnaDescription
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 (3)
Core 3
Core References
X_Refsource_Confirm x_refsource_confirm
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf
X_Refsource_Misc x_refsource_misc
https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
X_Refsource_Misc x_refsource_misc
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
Scores
CVSS v3
9.1
EPSS
0.0046
EPSS Percentile
36.2%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
yes
Technical Impact
partial
Details
CWE
CWE-113
Status
published
Products (3)
aio-libs/aiohttp
< 3.13.4
aiohttp/aiohttp
< 3.13.4
pypi/aiohttp
0 - 3.13.4PyPI
Published
Apr 01, 2026
Tracked Since
Apr 02, 2026