fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-107723
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-08 22:17:28 UTC
Updated2026-10-08 22:17:28 UTC
Descriptionfast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts a validly signed JWT whose payload is a JSON array because src/decoder.js checks that the payload is an object but does not reject arrays. The claim validator loop then finds no named exp, nbf, iss, aud, sub, jti, or nonce properties and silently skips those configured checks, returning the array as a successfully verified payload. An attacker who can produce or influence a validly signed token may bypass expiry, issuer, audience, subject, revocation, and replay protections. The opt-in requiredClaims option can block missing claims, and signature verification itself is not bypassed. This issue is fixed in version 6.3.0.

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from [email protected]

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

EPSS: 0.003580000 probability, percentile 0.275600000 (date 2026-10-09)

Problem Types: CWE-1287 | CWE-1287 CWE-1287: Improper Validation of Specified Type of Input

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Nearform Fast-jwt affected < 6.3.0 Not specified

References

ReferenceSourceLinkTags
github.com/nearform/fast-jwt/commit/86e83efd8b5244f50859532d99244f0a9a9a... [email protected] github.com
github.com/nearform/fast-jwt/releases/tag/v6.3.0 [email protected] github.com
github.com/nearform/fast-jwt/security/advisories/GHSA-5hjw-83fp-phq9 [email protected] github.com
github.com/nearform/fast-jwt/pull/639 [email protected] github.com
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