undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering
CVE-2026-109932
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.
Assessment
- CVSS
- 5.9 (v3.1)
- Severity
- Medium
- EPSS
- 0.00321% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 27 October 2026
- Last updated
- 27 October 2026
- Affected
- npm · undici
- Weakness
- CWE-400, CWE-405, CWE-770
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
At the source
References
- https://github.com/nodejs/undici/security/advisories/GHSA-9fm3-97px-rjf6
- https://nvd.nist.gov/vuln/detail/CVE-2026-109932
- https://github.com/nodejs/undici/commit/39f93e142df03e559fe7c3d1fc7fba9beee2c185
- https://github.com/nodejs/undici/commit/53944624462b6797560288c55dbd8c66857bb495
- https://github.com/nodejs/undici/commit/b217373bb024cd93f85eb5b3ffd25684855f60f8
- https://cna.openjsf.org/security-advisories.html
- https://github.com/nodejs/undici/releases/tag/v6.29.1
- https://github.com/nodejs/undici/releases/tag/v7.30.1
- https://github.com/nodejs/undici/releases/tag/v8.12.2
- https://github.com/advisories/GHSA-9fm3-97px-rjf6
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