CVE-2026-12151: undici WebSocket client vulnerable to denial of service via fragment count bypass

Vulnerability summary

CVE-2026-12151 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in nodejs undici. EPSS estimates a 0.79% chance of exploitation in the next 30 days, higher than 56.2% of scored vulnerabilities.

Timeline

1. 17-06-2026
   PublishedVulnerability first disclosed.
2. 11-09-2026
   Last modifiedVulnerability information updated.

Description

Impact: 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.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-770Allocation of Resources Without Limits or ThrottlingThe product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.