Executive brief
Centrifugo, a real-time messaging server, is vulnerable to a denial-of-service attack when using compressed WebSocket connections. An attacker can send a specially crafted, highly compressed message (a 'decompression bomb') that consumes excessive memory and CPU when the server attempts to process it. This can lead to server crashes or significant performance degradation, impacting the availability of real-time features for all users.
Technical details
A resource exhaustion vulnerability exists in Centrifugo's unidirectional WebSocket transport when 'uni_websocket.compression' is enabled. While the server enforced 'uni_websocket.message_size_limit' against the compressed wire-frame length, the 'ReadMessage' function used 'io.ReadAll' after decompression without an output cap. This allows an unauthenticated remote attacker to send a 'decompression bomb'—a small compressed payload that expands into a massive amount of data—triggering excessive memory and CPU consumption. The vulnerability is rooted in 'internal/websocket/conn.go' and 'internal/websocket/compression.go'. Version 6.8.4 fixes this by introducing 'decompressed_message_size_limit' to bound the size of messages after decompression.
Affected products
- Centrifugal Centrifugo < 6.8.4
Timeline
- 2026-06-28: patched: Fix committed to master branch
- 2026-06-30: advisory: GitHub Security Advisory published
- 2026-07-16: disclosed: CVE published to NVD