What’s Vulnerable › Vulnerabilities
CVE-2026-34950: fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key
- Severity: critical (CVSS 9.1 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-04-06 · updated 2026-10-26
- Weakness: CWE-327
Description
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.
Affected products
- nearform fast-jwt: before 6.2.0 — fixed in 6.2.0
How to fix
Upgrade to a fixed version: nearform fast-jwt 6.2.0. Check the vendor advisory for mitigations.
References
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