CVE-2026-35040: fast-jwt provides fast JSON Web Token (JWT) implementation

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MEDIUM 5.3REMOTEUPGRADE

CVE-2026-35040 is a medium-severity flaw (CVSS 5.3) affecting fast-jwt. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unintended behaviours. This is because some modifiers are stateful and will cause failures in every second verification attempt regardless of the validity of the token provided. Such modifiers are /g (global matchin

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 68%)
CISA exploited list	No
Weakness	CWE-440, CWE-697
Published	2026-04-09
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: nearform

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-09 16:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

nearform fast-jwt UPGRADE

Affected: < 6.2.1

Fixed in: 6.2.1

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls fast-jwt

2. UPGRADE to 6.2.1

npm install fast-jwt@">=6.2.1"

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-2026-35040?

fast-jwt: upgrade to 6.2.1. Exact commands for each OS are on this page.

Is CVE-2026-35040 being exploited?

CVE-2026-35040 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-2026-35040 affect?

CVE-2026-35040 affects fast-jwt. Severity is medium (CVSS 5.3). fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unint

How urgent is CVE-2026-35040?

Priority 37/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-35041 MEDIUM 4.2 UPGRADE fast-jwt provides fast JSON Web Token (JWT) implementation
CVE-2026-34950 CRITICAL 9.1 UPGRADE fast-jwt provides fast JSON Web Token (JWT) implementation
CVE-2026-35042 HIGH 7.5 UPGRADE fast-jwt provides fast JSON Web Token (JWT) implementation
CVE-2026-35039 CRITICAL 9.1 UPGRADE fast-jwt provides fast JSON Web Token (JWT) implementation

References

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