undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering

### Impact undici's WebSocket client (including Node.js's bundled `globalThis.WebSocket`) can be driven to exhaust process memory by a malicious or compromised WebSocket server. For every PING frame received, the receiver automatically writes a PONG response to the socket and ignores the `false` return value from `socket.write()`, which is a backpressure signal, so a server that streams small PING frames while never reading the client's PONGs makes the outbound write queue and heap grow without bound until the Node.js process runs out of memory and terminates. The attack is remote and unauthenticated, needs only a normal WebSocket connection, and is asymmetric: small inbound PINGs produce a much larger retained outbound queue. Availability is the only impact. undici 5.x, 6.x, 7.x, and 8.x are affected; the WebSocket client was introduced in 5.15.0. ### Patches Upgrade to `6.29.1`, `7.30.1`, or `8.12.2`, which pause WebSocket frame parsing when the automatic PONG response hits socket backpressure and resume on drain, bounding the outbound queue. ### Workarounds None.

Source published

27 Oct 2026 19:02:15 UTC

Source modified

27 Oct 2026 19:15:22 UTC

Observed here

27 Oct 2026 19:46:12 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · MODERATE