CVE-2026-9679: Impact: undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded

Q: How do I fix CVE-2026-9679?

undici: upgrade to 6.27.0, 7.28.0, 8.5.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-9679 being exploited?

CVE-2026-9679 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-2026-9679 affect?

CVE-2026-9679 affects undici. Severity is medium (CVSS 5.9). Impact: undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and bro

Q: How urgent is CVE-2026-9679?

Priority 30/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-9679 is a medium-severity flaw (CVSS 5.9) affecting undici. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Impact: undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either. Applications that parse a Set-Cookie header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 83%)
CISA exploited list	No
Weakness	CWE-93
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 18:18 UTCPublished CVE record published
2026-06-25 17:43 UTCUpdated Record last modified

nodejs undici UPGRADE

Affected: < 6.27.0 · >= 7.0.0 and < 7.28.0 · >= 8.0.0 and < 8.5.0

Fixed in: 6.27.0, 7.28.0, 8.5.0

Safe to downgrade to: a release before 7.0.0

1. Check installed version

npm ls undici

2. UPGRADE to 6.27.0

npm install undici@">=6.27.0"

3. If no update is available yet, DOWNGRADE to a release before 7.0.0

npm view undici versions npm install undici@"<7.0.0"

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-2026-9679?

undici: upgrade to 6.27.0, 7.28.0, 8.5.0. Exact commands for each OS are on this page.

Is CVE-2026-9679 being exploited?

CVE-2026-9679 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-2026-9679 affect?

CVE-2026-9679 affects undici. Severity is medium (CVSS 5.9). Impact: undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and bro

How urgent is CVE-2026-9679?

Priority 30/100. 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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