CVE-2026-69243: AIOHTTP: HTTP request smuggling via WebSocket upgrade

Severity: medium (CVSS 6.3 v4.0)
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: 2026-08-03 · updated 2026-10-23
Weakness: CWE-444

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.2, the HTTP parsers were vulnerable to a request smuggling attack relating to WebSocket upgrades. If using the server-side component, an attacker may be able to execute a request smuggling vulnerability using an edge case in the WebSocket upgrade procedure. A WebSocket upgrade request with a body could cause the parser to switch protocols before the complete request body was received, leaving trailing bytes to be handled as upgraded-protocol or pipelined data rather than normal HTTP body data. This issue is fixed in version 3.14.2.

Affected products

Pypi Aiohttp: before 3.14.2; 0.1, 0.10.0, 0.10.1, 0.10.2, 0.11.0, 0.12.0 (+302) — fixed in 3.14.2
aio-libs aiohttp: before 3.14.2

How to fix

Upgrade to a fixed version: Pypi Aiohttp 3.14.2. Check the vendor advisory for mitigations.

References

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