GHSA-38rv-x7px-6hhq undici WebSocket client vulnerable to denial of service via cumulative fragment bypass

• npm undici: >= 8.0.0, < 8.5.0 → fixed in 8.5.0

Impact The undici WebSocket client enforces `maxPayloadSize` per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service. Affected applications are those using the undici WebSocket client (`new WebSocket(...)`) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint. This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the `maxPayloadSize` feature and is also unaffected. Patches Upgrade to undici >= 8.5.0. Workarounds No workaround is available. The fix must be applied through an upgrade.