CVE-2026-34950: fast-jwt provides fast JSON Web Token (JWT) implementation

This week

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-34950 is a critical-severity flaw (CVSS 9.1) 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. In 6.1.0 and earlier, the publicKeyPemMatcher regex in fast-jwt/src/crypto.js uses a ^ anchor that is defeated by any leading whitespace in the key string, re-enabling the exact same JWT algorithm confusion attack that CVE-2023-48223 patched.

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 84%)
CISA exploited list	No
Weakness	CWE-327
Published	2026-04-06
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

2026-04-06 16:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

nearform fast-jwt UPGRADE

Affected: < 6.2.0

Fixed in: 6.2.0

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls fast-jwt

2. UPGRADE to 6.2.0

npm install fast-jwt@">=6.2.0"

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-2026-34950?

fast-jwt: upgrade to 6.2.0. Exact commands for each OS are on this page.

Is CVE-2026-34950 being exploited?

CVE-2026-34950 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-2026-34950 affect?

CVE-2026-34950 affects fast-jwt. Severity is critical (CVSS 9.1). fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, the publicKeyPemMatcher regex in fast-jwt/src/crypto.js uses a ^ anchor that is defeated by any leading whitespace in the key string, re-enabling the exact sa

How urgent is CVE-2026-34950?

Priority 46/100. Critical severity; 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-2026-35040 MEDIUM 5.3 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

← Back to latest CVEs