CVE-2023-49082: aiohttp's ClientSession is vulnerable to CRLF injection via method

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2023-11-29 · updated 2026-06-23
Weakness: CWE-20

Description

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. Improper validation makes it possible for an attacker to modify the HTTP request (e.g. insert a new header) or even create a new HTTP request if the attacker controls the HTTP method. The vulnerability occurs only if the attacker can control the HTTP method (GET, POST etc.) of the request. If the attacker can control the HTTP version of the request it will be able to modify the request (request smuggling). This issue has been patched in version 3.9.0.

Affected products

aio-libs aiohttp: before 3.9.0 — fixed in 3.9.0
Pypi Aiohttp: before 3.9.0; 0.1, 0.10.0, 0.10.1, 0.10.2, 0.11.0, 0.12.0 (+218) — fixed in 3.9.0

How to fix

Upgrade to a fixed version: aio-libs aiohttp 3.9.0; Pypi Aiohttp 3.9.0. Check the vendor advisory for mitigations.

References

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