CVE-2026-34520 LOW

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

Vendor Aio-Libs
Product aiohttp
Weakness CWE-113 · HTTP response splitting
Published April 1, 2026
Last update April 4, 2026
View on NVD All CVEs

CVSS base score

2.7/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS vector

CVSS: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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

April 1, 2026 CVE published
April 4, 2026 Record updated