Executive brief
Daphne, a popular web server for Django applications, is vulnerable to a denial-of-service attack. An unauthenticated remote attacker can send extremely large WebSocket messages that consume all available server memory. This can cause the server to crash or become unresponsive, disrupting service for all users.
Technical details
Daphne versions prior to 4.2.2 do not pass 'maxFramePayloadSize' or 'maxMessagePayloadSize' parameters to the underlying Autobahn WebSocketServerFactory. Since Autobahn defaults these values to 0 (unlimited), the server will attempt to buffer WebSocket frames and messages of any size into memory. A remote, unauthenticated attacker can exploit this by sending arbitrarily large WebSocket traffic, leading to resource exhaustion (CWE-770) and a denial of service (DoS). The issue is resolved in version 4.2.2 by properly configuring payload limits.
Affected products
- Django Software Foundation daphne < 4.2.2
Timeline
- 2026-06-03: disclosed
- 2026-06-03: advisory
- 2026-06-03: patched: Fixed in version 4.2.2