CVE-2025-53643: AIOHTTP is vulnerable to HTTP Request/Response Smuggling through incorrect parsing of chunked trailer sections

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-07-14 · updated 2026-06-17
Weakness: CWE-444

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.12.14, the Python parser is vulnerable to a request smuggling vulnerability due to not parsing trailer sections of an HTTP request. If a pure Python version of aiohttp is installed (i.e. without the usual C extensions) or AIOHTTP_NO_EXTENSIONS is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections. Version 3.12.14 contains a patch for this issue.

Affected products

aio-libs aiohttp: before 3.12.14 — fixed in 3.12.14
Pypi Aiohttp: before 3.12.14; 0.1, 0.10.0, 0.10.1, 0.10.2, 0.11.0, 0.12.0 (+292) — fixed in 3.12.14

How to fix

Upgrade to a fixed version: aio-libs aiohttp 3.12.14; Pypi Aiohttp 3.12.14. Check the vendor advisory for mitigations.

References

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