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

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Summary

CVECVE-2026-35042
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-06 17:17:13 UTC
Updated2026-04-06 17:17:13 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

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

Problem Types: CWE-345 | CWE-636 | CWE-345 CWE-345: Insufficient Verification of Data Authenticity | CWE-636 CWE-636: Not Failing Securely ('Failing Open')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Nearform Fast-jwt affected <= 6.1.0 Not specified

References

ReferenceSourceLinkTags
github.com/nearform/fast-jwt/security/advisories/GHSA-hm7r-c7qw-ghp6 [email protected] github.com
www.rfc-editor.org/rfc/rfc7515.html [email protected] www.rfc-editor.org
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NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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