by Kastro
Paper/Archive/CVE-2026-34520

CVE-2026-34520

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

EPSS 0.5%CVSS 9.1
critical.is priorityof 100
36
CVSS 9.1 (ADP)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 41.3.413 × 208.3No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
aiohttp< 3.13.4–CNA

Scores by source

CISA ADP9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
GitHub_M (CNA)2.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: partial

References

refgithub.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqfrefgithub.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4refgithub.com/aio-libs/aiohttp/releases/tag/v3.13.4