Medium severity · published Apr 1, 2026
CVE-2026-34519
AIOHTTP: HTTP response splitting via \r in reason phrase
5.3
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
AI
aiohttp · aio-libs
< 3.13.4 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34519
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-34519
Patch
https://github.com/aio-libs/aiohttp/commit/53b35a2f8869c37a133e60bf1a82a1c01642ba2b
Release Notes
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4
Patch
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mwh4-6h8g-pg8w
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