CVE-2026-59881

A flaw was found in AIOHTTP. The WebSocket client in AIOHTTP processes compressed data frames even when the compression mechanism, known as permessage-deflate, has not been properly negotiated. A malicious server can exploit this by sending specially crafted compressed frames. This can lead to unexpected and excessive consumption of the system's central processing unit (CPU) and memory, potentially resulting in a denial of service (DoS) for legitimate users.

Red Hat rates this flaw as Moderate with a CVSS score of 5.3 because exploitation requires an aiohttp WebSocket client to connect to an attacker-controlled server. In typical Red Hat product deployments, aiohttp serves as an HTTP client library for internal service communication rather than establishing WebSocket connections to untrusted endpoints. The resulting resource consumption is limited to the individual process running the affected client and does not propagate to other services or the host system.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

For deployments where upgrading is not immediately possible, ensure that aiohttp WebSocket clients only connect to trusted servers. The vulnerability requires the client to have opted out of permessage-deflate compression and the server to send RSV1-flagged frames, so connections using default compression settings are less likely to trigger this issue.