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CVE-2026-19534

HIGHCVSS 7.5/10EPSS 0.39%

Last modified

CVE-2026-19534 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. 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. EPSS estimates a 0.39% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
7.5/10

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

EPSS Probability
0.39%

33.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
NodejsUndici>= 6.7.0, < 6.28.1
NodejsUndici>= 7.0.0, < 7.29.1
NodejsUndici>= 8.0.0, < 8.10.2

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-19534?
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.
How severe is CVE-2026-19534?
CVE-2026-19534 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.39% probability of exploitation in the next 30 days.
How do I fix CVE-2026-19534?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST