CVE-2026-34519: AIOHTTP: HTTP response splitting via \r in reason phrase
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
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/aiohttpto a version that resolves this vulnerability.Fixed in 3.13.4 - Upgrade
Upgrade
aiohttpto a version that resolves this vulnerability.Fixed in 3.13.4Patch 53b35a2f8869c37a133e60bf1a82a1c01642ba2b