CVE-2026-42544: Granian vulnerable to unauthenticated DoS via WebSocket subprotocol header panic

May 6, 2026 (updated May 13, 2026)

Granian aborts a worker process when an unauthenticated client sends a WebSocket upgrade request whose Sec-WebSocket-Protocol header contains non-ASCII bytes.

The crash happens in Granian’s WebSocket scope construction path, before the ASGI application is invoked.

This is a single-request Denial Of Service against one worker. Repeating the request across workers takes the service offline.

References

github.com/advisories/GHSA-vrg7-482j-p6f6
github.com/emmett-framework/granian/security/advisories/GHSA-vrg7-482j-p6f6
nvd.nist.gov/vuln/detail/CVE-2026-42544

Code Behaviors & Features

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