CVE-2026-62963 in Centrifugo
Summary
by MITRE • 07/16/2026
Centrifugo is an open-source scalable real-time messaging server. Prior to 6.8.4, Centrifugo unidirectional WebSocket transport with uni_websocket.compression enabled enforced uni_websocket.message_size_limit against compressed wire-frame length in internal/websocket/conn.go advanceFrame, but ReadMessage used io.ReadAll after decompression without an output cap, allowing unauthenticated requests to /connection/uni_websocket to trigger large memory and CPU consumption. This issue is fixed in version 6.8.4.
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Analysis
by VulDB Data Team • 07/16/2026
The vulnerability in Centrifugo versions prior to 6.8.4 represents a critical resource exhaustion flaw that affects the server's WebSocket implementation. This weakness specifically impacts the uni_websocket transport mechanism when compression is enabled, creating a mismatch between input validation and actual processing behavior. The issue stems from inconsistent handling of message size limits between compressed and decompressed data streams, where the system validates against compressed frame length but processes uncompressed data without proper bounds checking.
The technical flaw manifests in the internal/websocket/conn.go file where the advanceFrame function enforces uni_websocket.message_size_limit against compressed wire-frame length. However, when ReadMessage is invoked, the system uses io.ReadAll to process decompressed data without applying any output capacity restrictions. This design inconsistency allows attackers to send carefully crafted compressed messages that appear below the size threshold when compressed but expand to enormous sizes upon decompression. The vulnerability enables unauthenticated attackers to trigger excessive memory allocation and CPU consumption through requests to the /connection/uni_websocket endpoint.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can lead to complete service disruption and potential denial of service conditions for legitimate users. Attackers can leverage this flaw to consume system resources proportional to the decompression expansion ratio, potentially causing memory allocation failures, garbage collection overhead, and overall system instability. The issue affects any Centrifugo deployment using the uni_websocket transport with compression enabled, making it particularly dangerous in production environments where resource constraints are already tight.
Mitigation strategies should focus on upgrading to version 6.8.4 or later, which addresses the core inconsistency by implementing proper output caps during decompression processes. Organizations should also consider implementing additional monitoring for unusual memory and CPU consumption patterns, particularly around WebSocket connections. Network-level controls such as rate limiting and connection pooling can provide additional protection layers. This vulnerability aligns with CWE-770 (Allocation of Resources Without Limits or Throttling) and represents a classic example of how compression-related security flaws can amplify resource consumption attacks, similar to issues documented in the ATT&CK framework under privilege escalation and resource exhaustion techniques.