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TI-2026-27174 Aliases CVE-2026-34950GHSA-mvf2-f6gm-w987

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

Priority HIGH 80CWE-327Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Information disclosure
Confidentiality · integrity · availability
High · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-327.

Summary

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 it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.0025 16th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed fast-jwt (npm): 6.2.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
nearformfast-jwtup to 6.1.0—No fix listedCNA
—fast-jwt (npm)before 6.2.06.2.0Patch availableGHSA-mvf2-f6gm-w987
  • fast-jwt Vendornearform Affected up to 6.1.0 Fixed in — No fix listed CNA
  • fast-jwt (npm) Vendor— Affected before 6.2.0 Fixed in 6.2.0 Patch available GHSA-mvf2-f6gm-w987

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:*before 6.2.0Vulnerablenearform
  • cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:* Versions before 6.2.0 Vulnerable ·nearform

Remediation

  • Fix · GHSA-mvf2-f6gm-w987 fast-jwt (npm) Fixed in 6.2.0 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-34950
  2. 2026-10-03 Alias added: GHSA-mvf2-f6gm-w987

References

Exploit 1

Advisory 2

Other 1

  • TI-2026-27245 fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation) CVSS 3.1HIGH 7.5
  • TI-2026-27243 fast-jwt: Stateful RegExp (/g or /y) causes non-deterministic allowed-claim validation (logical DoS) CVSS 3.1MEDIUM 5.3
  • TI-2026-27244 ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification CVSS 3.1MEDIUM 6.5
  • TI-2026-27242 Insufficient verification of data authenticity in nearform fast-jwt CVSS 3.1CRITICAL 9.1
  • TI-2023-26087 fast-jwt JWT Algorithm Confusion CVSS 3.1MEDIUM 5.9

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences