Denial of Service due to unbounded memory growth via WebSocket frames

Summary

The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively 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(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint. All releases starting at undici 6.17.0 are affected. Patches: Upgrade to undici >= 6.26.0, >= 7.28.0, or >= 8.5.0. Workarounds: No workaround is available. The fix must be applied through an upgrade. A flaw was found in undici. A malicious WebSocket server can exploit this by streaming numerous small or empty continuation frames. This can bypass per-frame and cumulative-size validation, leading to unbounded memory growth in the client process. The primary consequence is memory exhaustion, resulting in a denial of service (DoS) for affected applications using the undici WebSocket client or WebSocketStream API. This Important denial of service flaw in the `undici` WebSocket client allows a remote attacker to cause unbounded memory growth. By sending numerous small or empty WebSocket frames, an unauthenticated attacker can exhaust system memory, leading to a denial of service in Red Hat products that use the affected client. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-770. Fixed by RHSA-2026:35841, RHSA-2026:35842, RHSA-2026:34342 — update the affected packages (`sudo dnf update`). Affected Red Hat products: Red Hat Enterprise Linux 10; Cluster Observability Operator 1.5.0. Will not fix / out of support: Red Hat Hardened Images.