AIOHTTP: WebSocket client accepts compressed frames without negotiated permessage-deflate
Summary
The client accepts and decompresses frames with the RSV1 bit set even when the permessage-deflate extension was not negotiated.
Impact
A client may unexpectedly decompress WebSocket frames when explicitly opted out. This could lead to additional CPU/memory consumption, but is unlikely to be a significant issue unless a zip bomb vulnerability or similar is also present.
Patch: https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | aiohttp | < 3.14.2 | 3.14.2 |
References
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-mq44-7p77-q5h7
- https://nvd.nist.gov/vuln/detail/CVE-2026-59881
- https://github.com/aio-libs/aiohttp/pull/12978
- https://github.com/aio-libs/aiohttp/commit/47fb6ae354d4fa22048f4dbe7dbf82b625f0a2f6
- https://github.com/aio-libs/aiohttp
- http://github.com/aio-libs/aiohttp/releases/tag/v3.14.2
- https://pypi.org/project/aiohttp
- https://github.com/advisories/GHSA-mq44-7p77-q5h7
- CVSS 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- Weakness (CWE)
CWE-20- Platform
- Python (PyPI)
- Package
aiohttp- Disclosed
- 03.08.2026
- Updated
- 11.10.2026 15:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3547 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-mq44-7p77-q5h7 - CC BY 4.0
Vulnerability history: aiohttp
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 55
- First → latest
- 02.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 7
- Medium 29
- Low 19
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 6
- 2024: 7
- 2025: 1
- 2026: 40
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AIOHTTP: WebSocket client accepts compressed frames without negotiated permessage-deflate this entry
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