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Vulnerability record · CVE-2026-34950 · published 6 April 2026

CVE-2026-34950: Nearform fast-jwt broken cryptographic algorithm vulnerability

Nearform · Fast Jwt

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.

9.1 CVSS 3.1 Critical EPSS 0.27% · top 82.2% CWE-327 · Broken cryptographic algorithm
9.1CVSS 3.1 base score
0.27%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References, 1 tagged exploit
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/nearform/fast-jwt/security/advisories/GHSA-mvf2-f6gm-w987 ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.1CVE-2026-35039Nearform fast-jwt insufficient verification of data authenticity vulnerabilityfast-jwt provides fast JSON Web Token (JWT) implementation. From 0.0.1 to before 6.2.0, setting up a custom cacheKeyBuilder method which does not pro…EPSS 0.22%7.5CVE-2026-35042Nearform fast-jwt insufficient verification of data authenticity vulnerabilityfast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter def…EPSS 0.20%6.5CVE-2026-35041Nearform fast-jwt inefficient regular expression (redos) vulnerabilityfast-jwt provides fast JSON Web Token (JWT) implementation. From 5.0.0 to 6.2.0, a denial-of-service condition exists in fast-jwt when the allowedAud…EPSS 0.43%5.9CVE-2023-48223Nearform fast-jwt improper input validation vulnerabilityfast-jwt provides fast JSON Web Token (JWT) implementation. Prior to version 3.3.2, the fast-jwt library does not properly prevent JWT algorithm conf…EPSS 0.68%5.3CVE-2026-35040Nearform fast-jwt vulnerabilityfast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, …EPSS 0.63%

Source: NIST National Vulnerability Database (record CVE-2026-34950), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.