CVE-2026-9675: Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size

Q: How do I fix CVE-2026-9675?

undici: upgrade to 8.5.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-9675 being exploited?

CVE-2026-9675 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-2026-9675 affect?

CVE-2026-9675 affects undici. Severity is high (CVSS 7.5). Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame valida

Q: How urgent is CVE-2026-9675?

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

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-9675 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.

Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service. Affected applications are those using the undi

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 63%)
CISA exploited list	No
Weakness	CWE-400, CWE-770
Published	2026-06-17
Last modified	2026-06-25

Publisher (CNA): openjs · Vendor: nodejs

Last updated 2026-06-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-17 17:17 UTCPublished CVE record published
2026-06-25 17:46 UTCUpdated Record last modified

nodejs undici UPGRADE

Affected: >= 8.0.0 and < 8.5.0

Fixed in: 8.5.0

Safe to downgrade to: a release before 8.0.0

1. Check installed version

npm ls undici

2. UPGRADE to 8.5.0

npm install undici@">=8.5.0"

3. If no update is available yet, DOWNGRADE to a release before 8.0.0

npm view undici versions npm install undici@"<8.0.0"

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-2026-9675?

undici: upgrade to 8.5.0. Exact commands for each OS are on this page.

Is CVE-2026-9675 being exploited?

CVE-2026-9675 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-2026-9675 affect?

CVE-2026-9675 affects undici. Severity is high (CVSS 7.5). Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame valida

How urgent is CVE-2026-9675?

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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