CVE-2026-9675
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk34th percentile — higher than 34% of all known CVEs
Summary
The undici WebSocket client in version 8.1.0 does not enforce the cumulative size of fragmented uncompressed messages, leading to unbounded memory growth. A malicious WebSocket server can stream many small fragments that pass validation but collectively exceed the configured limit, resulting in memory exhaustion and denial of service.
Risk Assessment
Organizations using the undici WebSocket client in version 8.1.0 are vulnerable to attacks that can lead to memory exhaustion and application downtime. The risk increases when connecting to an attacker-controlled endpoint.
Recommendation
It is recommended to upgrade to undici >= 8.5.0 to mitigate this vulnerability. No workarounds are available, so an upgrade is necessary.
Original NVD description (English source)
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.