# CVE-2026-59881: aio-libs aiohttp resource exhaustion in WebSocket client decompression

Source: https://junglewise.ai/threats/cve-2026-59881-aio-libs-aiohttp-resource-exhaustion-in-websocket-client  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-30. Updated: 2026-08-03  
License: CC BY 4.0 with a link back

CVE-2026-59881 · Severity: medium · CVSS 4 · Published 2026-07-30

A vulnerability exists in the aiohttp library, a popular Python framework for building web services and clients. The WebSocket client component incorrectly processes compressed data even when it has been configured not to do so. This could allow a malicious server to force the client to perform intensive decompression tasks, potentially leading to high CPU and memory usage that could slow down or crash the application.

Technologies: [aiohttp (PyPI)](https://junglewise.ai/threats/technologies/aiohttp). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-59881 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59881 being exploited in the wild.

**How severe is CVE-2026-59881?** Medium severity, with a CVSS score of 4, published 30 July 2026.

**Which products and versions are affected?** aiohttp (PyPI) <= 3.14.1, ECOSYSTEM:introduced=0,fixed=3.14.2.

**Is there a fix for CVE-2026-59881?** Yes. aiohttp (PyPI): upgrade to 3.14.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-59881 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59881?** Check whether you run aiohttp (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- aiohttp (PyPI): upgrade to 3.14.2 or later

  ```sh
  pip install "aiohttp>=3.14.2"
  ```


## Technical details

A vulnerability in aiohttp's WebSocket client implementation involves improper input validation of the RSV1 bit in WebSocket frames. The client fails to verify if the 'permessage-deflate' extension was successfully negotiated before attempting to decompress frames marked with the RSV1 bit. An attacker-controlled WebSocket server can send unsolicited compressed frames to a connected aiohttp client, forcing decompression. This can be leveraged to cause resource exhaustion (CPU/memory), particularly if combined with highly compressed payloads (zip bombs). The issue is fixed in version 3.14.2.

## Affected products

- aio-libs aiohttp <= 3.14.1

## Identifiers

- CVE-2026-59881
- GHSA-mq44-7p77-q5h7
- PYSEC-2026-3547

## Timeline

- 2026-07-26: disclosed: Initial disclosure by Dreamsorcerer
- 2026-07-30: advisory: NVD published CVE-2026-59881
- 2026-08-03: patched: GitHub Advisory published and version 3.14.2 released

## References

- [https://api.github.com/users/gik2927](https://api.github.com/users/gik2927)
- [https://github.com/gik2927](https://github.com/gik2927)
- [https://api.github.com/users/gik2927/gists%7B/gist_id%7D](https://api.github.com/users/gik2927/gists%7B/gist_id%7D)
- [https://api.github.com/users/gik2927/repos](https://api.github.com/users/gik2927/repos)
- [https://avatars.githubusercontent.com/u/59925086?v=4](https://avatars.githubusercontent.com/u/59925086?v=4)
- [https://api.github.com/users/gik2927/events%7B/privacy%7D](https://api.github.com/users/gik2927/events%7B/privacy%7D)

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