Is CVE-2026-35040 in the CISA KEV catalog?

No. CVE-2026-35040 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-35040?

CVE-2026-35040 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-35040?

CVE-2026-35040 has an EPSS score of 0.38% (30th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-35040?

Upgrade fast-jwt to 6.2.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-35040

MEDIUM

5.3

CVSS v3

NVD

Description

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unintended behaviours. This is because some modifiers are stateful and will cause failures in every second verification attempt regardless of the validity of the token provided. Such modifiers are /g (global matching) and /y (sticky matching). This does NOT allow invalid tokens to be accepted, only for valid tokens to be improperly rejected in some configurations. Instead it causes 50% of valid authentication requests to fail in an alternating pattern. This vulnerability is fixed in 6.2.1.

CWE-440 CWE-697

How to fix

Remediation Available

fast-jwtNVD

Affected:< 6.2.1Fixed in:6.2.1CVE-2026-35040derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

0.38%probability of exploitation in 30 days

30thpercentile

Low risk: more likely to be exploited than 30% of all known CVEs.

References

Patch2

Exploit1

github.com

Release Notes1

github.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-17.