Vulnerability · Published Jul 30, 2026 · Assigned by GitHub_M

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

Medium 6.9

In plain English

A medium-severity improper input validation in aiohttp from aio-libs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.9Medium

Exploit odds (30 days)0.5%top 55.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	python-aiohttp	3.8.4-1+deb12u2	DEBIAN-CVE-2026-59881
Debian:13	python-aiohttp	no fix listed	DEBIAN-CVE-2026-59881
Debian:14	python-aiohttp	3.14.3-1	DEBIAN-CVE-2026-59881
PyPI	aiohttp	3.14.2	GHSA-mq44-7p77-q5h7
PyPI	aiohttp	3.14.2	PYSEC-2026-3547
Ubuntu:26.10	python-aiohttp	no fix listed	UBUNTU-CVE-2026-59881

Affected products (as reported)

Vendor	Product	Versions
aio-libs	aiohttp	< 3.14.2

Weakness: CWE-20 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

References

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