CVE-2026-19534: undici's WebSocket client crashes the whole Node.js process during the opening handshake when a server respond

Q: How do I fix CVE-2026-19534?

undici: upgrade to 6.28.1, 7.29.1, 8.10.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-19534 being exploited?

CVE-2026-19534 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-19534 affect?

CVE-2026-19534 affects undici. Severity is high (CVSS 7.5). 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

Q: How urgent is CVE-2026-19534?

Priority 40/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-19534 is a high-severity flaw (CVSS 7.5) affecting undici. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 67%)
CISA exploited list	No
Weakness	CWE-248, CWE-252
Published	2026-09-04
Last modified	2026-09-16

Publisher (CNA): openjs · Vendor: nodejs

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-04 18:17 UTCPublished CVE record published
2026-09-16 20:41 UTCUpdated Record last modified

nodejs undici UPGRADE

Affected: >= 6.7.0 and < 6.28.1 · >= 7.0.0 and < 7.29.1 · >= 8.0.0 and < 8.10.2

Fixed in: 6.28.1, 7.29.1, 8.10.2

Safe to downgrade to: a release before 6.7.0

1. Check installed version

npm ls undici

2. UPGRADE to 6.28.1

npm install undici@">=6.28.1"

3. If no update is available yet, DOWNGRADE to a release before 6.7.0

npm view undici versions npm install undici@"<6.7.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-19534?

undici: upgrade to 6.28.1, 7.29.1, 8.10.2. Exact commands for each OS are on this page.

Is CVE-2026-19534 being exploited?

CVE-2026-19534 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-19534 affect?

CVE-2026-19534 affects undici. Severity is high (CVSS 7.5). 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

How urgent is CVE-2026-19534?

Priority 40/100. High severity; Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities

Related CVEs

CVE-2026-109855 HIGH 7.5 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109383 HIGH 7.4 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109829 HIGH 7.4 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109841 MEDIUM 5.9 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109869 HIGH 7.5 UPGRADE undici is an HTTP client library for Node.js

References

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