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CVE-2026-35042

Nearform Fast-jwt vulnerability

7.5 HIGHPublic exploitEPSS 0.20%
  1. Published6 Apr 2026

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

Nearform Fast-jwt< 6.2.0

Remediation

Fixed in
Nearform Fast-jwt≥ 6.2.0

References

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Frequently asked

Is CVE-2026-35042 being actively exploited?

CVE-2026-35042 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.20%.

How severe is CVE-2026-35042?

CVE-2026-35042 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.20% probability of exploitation.

Which products are affected by CVE-2026-35042?

Affected products include Nearform Fast-jwt.

How do I fix CVE-2026-35042?

Upgrade affected software to a fixed version, for example Nearform Fast-jwt 6.2.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.