CVE-2026-34520CWE-113

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

Low · published April 1, 2026

CVSS v4.0
2.7
EPSS
1%
Percentile
51.7
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
2.7 · LOW
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
EPSS
0.00676 · 51.7th percentile
Weakness
CWE-113 · Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
Published
2026-04-01T20:27Z
EPSS history
Timeline
  • 01 APR 20:27Z
    AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass
    cvelistv5