CVE-2026-109855: undici is an HTTP client library for Node.js

Q: How do I fix CVE-2026-109855?

undici: upgrade to 8.11.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-109855 being exploited?

CVE-2026-109855 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-2026-109855 affect?

CVE-2026-109855 affects undici. Severity is high (CVSS 7.5). undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already

Q: How urgent is CVE-2026-109855?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-109855 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 is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the connection, the orphaned stream emits an unhandled

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	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-248, CWE-754
Published	2026-10-15
Last modified	2026-10-19

Publisher (CNA): openjs · Vendor: nodejs

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-10-15 09:17 UTCPublished CVE record published
2026-10-19 20:46 UTCUpdated Record last modified

nodejs undici UPGRADE

Affected: >= 8.11.0 and < 8.11.2

Fixed in: 8.11.2

Safe to downgrade to: a release before 8.11.0

1. Check installed version

npm ls undici

2. UPGRADE to 8.11.2

npm install undici@">=8.11.2"

3. If no update is available yet, DOWNGRADE to a release before 8.11.0

npm view undici versions npm install undici@"<8.11.0"

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-2026-109855?

undici: upgrade to 8.11.2. Exact commands for each OS are on this page.

Is CVE-2026-109855 being exploited?

CVE-2026-109855 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-2026-109855 affect?

CVE-2026-109855 affects undici. Severity is high (CVSS 7.5). undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already

How urgent is CVE-2026-109855?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities

Related CVEs

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
CVE-2026-109924 MEDIUM 5.9 UPGRADE undici is an HTTP client library for Node.js

References

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