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TI-2026-27245 Aliases CVE-2026-35042GHSA-hm7r-c7qw-ghp6

fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)

Priority HIGH 72CWE-345Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
None · High · None
Fix status
No fix listed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-345.

Summary

fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that fast-jwt does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00158 4th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

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)up to 6.1.0—No fix listedGHSA-hm7r-c7qw-ghp6
  • fast-jwt Vendornearform Affected up to 6.1.0 Fixed in — No fix listed CNA
  • fast-jwt (npm) Vendor— Affected up to 6.1.0 Fixed in — No fix listed GHSA-hm7r-c7qw-ghp6

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

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-35042
  2. 2026-10-03 Alias added: GHSA-hm7r-c7qw-ghp6

References

Exploit 1

Advisory 2

Other 2

  • TI-2026-27174 fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key CVSS 3.1CRITICAL 9.1
  • 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