CVE-2026-34519: AIOHTTP: HTTP response splitting via \r in reason phrase
Published Apr 1, 2026
·Updated
Summary
An attacker who controls the reason parameter when creating a Response may be able to inject extra headers or similar exploits.
Impact
In the unlikely situation that an application allows untrusted data to be used in the response's reason parameter, then an attacker could manipulate the response to send something different from what the developer intended.
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Patch: https://github.com/aio-libs/aiohttp/commit/53b35a2f8869c37a133e60bf1a82a1c01642ba2b
Other sources
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, an attacker who controls the reason parameter when creating a Response may be able to inject extra headers or similar exploits. This issue has been patched in version 3.13.4.
— MITRE
Affected Software
2 affected componentsFixes available
pip/aiohttp<=3.13.3
3.13.4
aiohttp aiohttp<3.13.4
Remediation
Event History
Apr 1, 2026
CVE Published
via MITRE·08:26 PM
Data Sourced
via MITRE·08:26 PM
DescriptionWeakness
Data Sourced
via NVD·09:17 PM
DescriptionSeverityWeakness
Data Sourced
via NVD·09:17 PM
RemedyAffected Software
Advisory Published
via GitHub·09:48 PM
Data Sourced
via GitHub·09:48 PM
DescriptionWeaknessAffected Software