# CVE-2026-19534: undici vulnerable to Denial of Service via unrequested WebSocket subprotocol

> CVE-2026-19534: undici vulnerable to Denial of Service via unrequested WebSocket subprotocol. CVSS 7.5 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-19534
Last updated: 2026-09-16T20:41:08Z

- Published: 2026-09-04 17:10 UTC · Updated: 2026-09-16 20:41 UTC · Assigner: openjs
- CVSS: 7.5 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS: 0.39%, 33th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-248, CWE-252

## Description

undici's WebSocket client crashes the whole Node.js process during the opening handshake when a server responds with a subprotocol that the client never requested. A default WebSocket connection sends no subprotocol, but if the server's 101 response includes a Sec-WebSocket-Protocol header, undici dereferences a null value while checking it against the requested list and throws an uncaught TypeError. Because that code runs inside a microtask with no surrounding error handling, the exception propagates and terminates the process under Node's default behavior, instead of gracefully failing the connection as required by the WebSocket protocol. Any application that opens a WebSocket to an attacker-controlled or compromised server, or over a plaintext connection subject to a machine-in-the-middle, can be crashed remotely without authentication in the default configuration. This affects undici versions from 6.7.0 up to 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

## Affected vendors and products

- undici: undici

## Tracked companies

- [Jira](https://rewindex.com/company/jira.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-19534)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-19534)
- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/nodejs/undici/security/advisories/GHSA-rfgv-xxqx-mfg5](https://github.com/nodejs/undici/security/advisories/GHSA-rfgv-xxqx-mfg5)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-19534 · Markdown: https://rewindex.com/cve/CVE-2026-19534.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-19534 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:16:21.794Z