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CVE-2026-34520

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

Published: Apr 1, 2026Updated: Apr 16, 2026 Sources: CVE List NVDCWE-113
NVD MITRE
9.1CVSSCRITICAL
EPSS Score
0.5%
Top 63.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

Description

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-113

Affected Products

aiohttpaio-libs
Library
OSS Libraries / web-framework
aiohttpaiohttp
Library
OSS Libraries / web-framework
aio-libsoss-projectOSS Librariesaka aiohttp, aiosmtpd, aiohttp session
aiohttposs-projectOSS Libraries

Exploitability

Official Patch Available

References

https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf
github.com
https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4
github.com
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
github.com

Timeline

Published
Apr 1, 2026
Last Updated
Apr 16, 2026

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