Cyber Resilience

CVE-2026-35040

Nearform Fast-Jwt ≤ 6.2.1

Public PoC
Published
09 April 2026
Modified
17 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS Score 0.0038 31th percentile
Risk Priority 44 floored blend · peak EPSS

Summary

CVE-2026-35040 is a medium-severity Expected Behavior Violation (CWE-440) vulnerability in Nearform Fast-Jwt. Its CVSS base score is 5.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Obfuscated Files or Information (T1027); ranked at the 31th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-6 (Security and Privacy Function Verification) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

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…

more

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(s)
CWE-440CWE-697

Related Threats

MITRE ATT&CK Enterprise Techniques

T1027 Obfuscated Files or Information Stealth
Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-48223Same product: Nearform Fast-Jwt
CVE-2026-35039Same product: Nearform Fast-Jwt
CVE-2026-35042Same product: Nearform Fast-Jwt
CVE-2026-34950Same product: Nearform Fast-Jwt
CVE-2026-35041Same product: Nearform Fast-Jwt
CVE-2024-24556Same vendor: Nearform
CVE-2024-39534Shared CWE-697
CVE-2023-23766Shared CWE-697
CVE-2025-12192Shared CWE-697
CVE-2023-46009Shared CWE-697

Affected Assets

nearform
fast-jwt
≤ 6.2.1

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation directly checks whether implemented functions match their specifications.

SI-6 Security and Privacy Function Verification good match

Security function verification confirms that functions operate according to their defined expected behavior.

AC-25 Reference Monitor partial match

A reference monitor must be small and correct, structurally limiting the chance of flawed comparison logic in authorization decisions.

SA-17 Developer Security and Privacy Architecture and Design partial match

Requiring a documented security architecture and design reduces the chance that implementation deviates from intended behavior.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles require correct implementation of comparison logic used for access and authentication decisions.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 full match
prevents

Secure SDLC practices directly enforce specification compliance and catch expected-behavior violations during development.

ID.IM-02 partial match
prevents

Security testing and exercises help discover behavior deviations before deployment.

ID.RA-01 partial match
prevents

Vulnerability identification can surface spec-violating flaws, while eliminating the weakness reduces some vulnerability backlog.

PR.PS-02 partial match
prevents

Routine software maintenance and patching can remediate discovered specification violations.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development and acceptance validates that functions behave as specified.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates verification against specifications, directly reducing expected-behavior violations.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly define expected behavior that must be met.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles can require robust comparison mechanisms for access decisions.

A.8.28 Secure coding partial match
prevents

Secure coding practices enforce adherence to functional specifications during implementation.

A.8.32 Change management partial match
finds

Change management can catch specification deviations introduced by modifications.

References