What’s Vulnerable › Vulnerabilities

CVE-2026-59881: AIOHTTP: WebSocket client accepts compressed frames without negotiated permessage-deflate

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-30 · updated 2026-10-23
• Weakness: CWE-20

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.2, the WebSocket client accepts and decompresses frames with the RSV1 bit set even when the permessage-deflate extension was not negotiated, allowing a malicious server to cause unexpected CPU and memory consumption. 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

• http://github.com/aio-libs/aiohttp/releases/tag/v3.14.2
• https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6
• https://github.com/aio-libs/aiohttp/pull/12978
• https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mq44-7p77-q5h7

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