undici's WebSocket client, including Node.js's bundled globalThis.WebSocket, is vulnerable to a denial of service condition caused by unbounded automatic PONG buffering. A malicious WebSocket server can send continuous PING frames causing the client to queue PONG responses without respecting backpressure, leading to memory exhaustion and process termination. This affects undici versions from 5.15.0 up to but not including 6.29.1, 7.0.0 up to 7.30.1, and 8.0.0 up to 8.12.2. Upgrading to versions 6.29.1, 7.30.1, or 8.12.2 mitigates the issue by properly handling backpressure.