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GHSA-vxpw-j846-p89q

undici WebSocket client vulnerable to denial of service via fragment count bypass

Source: GitHub Advisory Database (reviewed) High CVE-2026-12151

Packages

EcosystemPackageAffectedFixed in
npm undici < 6.27.0 6.27.0
npm undici >= 7.0.0, < 7.28.0 7.28.0
npm undici >= 8.0.0, < 8.5.0 8.5.0

Details

As written in the advisory (Markdown source, shown as plain text).

## 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 v6.27.0, v7.28.0 or v8.5.0. ## Workarounds No workaround is available. The fix must be applied through an upgrade.

References

External links from the advisory. They lead to third-party sites.