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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
9.1CRITICAL
NVD MITRE
EPSS Score
0.5%
Top 62.3%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

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.

No summary for this CVE yet.

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

aio-libs
oss-projectaka aiohttp, aiosmtpd, aiohttp session
aiohttpLibrary
OSS Libraries / web-framework
aiohttp
oss-project
aiohttpLibrary
OSS Libraries / web-framework

Exploitability

Official Patch Available
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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

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