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TI-2026-69689 Aliases CVE-2026-107720GHSA-8wpc-h4q6-8fxv

fast-jwt accepts unsigned JWTs when the key is empty or null

Priority HIGH 68CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
Security bypass
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-347.

Summary

fast-jwt before 6.3.1 is affected. When createVerifier receives an empty string or null key together with a non-empty algorithms allowlist, it accepts unsigned JWTs (CWE-347). A remote attacker without a signing key can submit a token with arbitrary claims, which can lead to authentication or authorization bypass. Claim validators still run, and non-empty keys are not affected.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00324 25th percentileScored 2026-11-07
Fix Fixed fast-jwt (nearform): 6.3.1fast-jwt (npm): 6.3.1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
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-jwtbefore 6.3.16.3.1Patch availableCNA
—fast-jwt (npm)before 6.3.16.3.1Patch availableGHSA-8wpc-h4q6-8fxv
  • fast-jwt Vendornearform Affected before 6.3.1 Fixed in 6.3.1 Patch available CNA
  • fast-jwt (npm) Vendor— Affected before 6.3.1 Fixed in 6.3.1 Patch available GHSA-8wpc-h4q6-8fxv

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:*:*:*——nearform
  • cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:*:*:* Versions — — ·nearform

Remediation

Upgrade the npm fast-jwt package to version 6.3.1. The sources list no fixed version for nearform fast-jwt.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

  • Fix · CNA fast-jwt (nearform) Fixed in 6.3.1
  • Fix · GHSA-8wpc-h4q6-8fxv fast-jwt (npm) Fixed in 6.3.1 Advisory →

Timeline

  1. 2026-10-09 Threatist record created from CVE-2026-107720
  2. 2026-10-09 Alias added: GHSA-8wpc-h4q6-8fxv
  3. 2026-10-10 CISA SSVC decision points changed
  4. 2026-10-10 Priority changed: MEDIUM → HIGH

References

Other 5

  • TI-2026-69702 Incomplete fix in fast-jwt enables RSA to HS256 algorithm confusion CVSS 3.1CRITICAL 9.8
  • 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-2025-37324 get-jwks poisoned JWKS cache allows post-fetch issuer validation bypass CVSS 3.0CRITICAL 9.4
  • TI-2026-27245 fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation) CVSS 3.1HIGH 7.5
  • TI-2026-69684 Claim validator bypass in fast-jwt when JWT payload is a JSON array CVSS 3.1HIGH 8.1
  • TI-2026-69695 fast-jwt accepts public JWK JSON as HMAC key, enabling token forgery CVSS 3.1HIGH 7.4
See all 15 →

Sources

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