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TI-2026-27244 Aliases CVE-2026-35041GHSA-cjw9-ghj4-fwxf

ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification

Priority MEDIUM 62CWE-1333Published · Updated

Key facts

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

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and GitHub. Impact type from CWE-1333.

Summary

fast-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 verification option is configured using a regular expression. Because the aud claim is attacker-controlled and the library evaluates it against the supplied RegExp, a crafted JWT can trigger catastrophic backtracking in the JavaScript regex engine, resulting in significant CPU consumption during verification. This vulnerability is fixed in 6.2.1.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00272 19th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed fast-jwt (nearform): 6.2.1fast-jwt (npm): 6.2.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
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-jwt5.0.0 to before 6.2.16.2.1Patch availableCNA
—fast-jwt (npm)5.0.0 to before 6.2.16.2.1Patch availableGHSA-cjw9-ghj4-fwxf
  • fast-jwt Vendornearform Affected 5.0.0 to before 6.2.1 Fixed in 6.2.1 Patch available CNA
  • fast-jwt (npm) Vendor— Affected 5.0.0 to before 6.2.1 Fixed in 6.2.1 Patch available GHSA-cjw9-ghj4-fwxf

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:*5.0.0 to before 6.2.1Vulnerablenearform
  • cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:* Versions 5.0.0 to before 6.2.1 Vulnerable ·nearform

Remediation

  • Fix · CNA fast-jwt (nearform) Fixed in 6.2.1
  • Fix · GHSA-cjw9-ghj4-fwxf fast-jwt (npm) Fixed in 6.2.1 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-35041
  2. 2026-10-03 Alias added: GHSA-cjw9-ghj4-fwxf

References

Exploit 1

Patch 2

Advisory 1

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-2026-27245 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-2026-27242 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