by Kastro
Paper/Archive/CVE-2026-34950

CVE-2026-34950

nearform fast-jwt — fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key

EPSS 0.2%public exploitCVSS 9.1
critical.is priorityof 100
41
CVSS 9.1 (CNA)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 15.8.158 × 203.2Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
fast-jwt<= 6.1.0–CNA

Scores by source

GitHub_M (CNA)9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: total

References

refgithub.com/nearform/fast-jwt/security/advisories/GHSA-mvf2-f6gm-w987