CVE-2026-35042
Nearform Fast-Jwt ≤ 6.2.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NSummary
CVE-2026-35042 is a high-severity Insufficient Verification of Data Authenticity (CWE-345) vulnerability in Nearform Fast-Jwt. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Mark-of-the-Web Bypass (T1553.005); ranked at the 5th 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 CP-12 (Safe Mode) and SC-23 (Session Authenticity) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-35042 is a vulnerability in the fast-jwt library, a fast JSON Web Token (JWT) implementation for Node.js, affecting versions 6.1.0 and earlier. The issue stems from improper validation of the "crit" (Critical) Header Parameter as specified in RFC 7515 §4.1.11. When a JWS token includes a "crit" array listing extensions that fast-jwt does not recognize, the library accepts the token instead of rejecting it, violating the RFC's MUST requirement to reject such tokens. This flaw is classified under CWE-345 (Insufficient Verification of Data Authenticity) and CWE-636 (Not Failing Securely ("Failing Open")), with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).
Remote attackers require no privileges or user interaction and can exploit this over the network with low attack complexity. By crafting a JWS token with a "crit" header listing unrecognized extensions, an attacker can cause fast-jwt to accept the token despite the security violation, potentially enabling integrity compromises such as bypassing intended JWT validation controls in applications relying on the library.
The primary GitHub security advisory at https://github.com/nearform/fast-jwt/security/advisories/GHSA-hm7r-c7qw-ghp6 details the issue and mitigation steps. Additional technical reference is provided in RFC 7515 §4.1.11 at https://www.rfc-editor.org/rfc/rfc7515.html#section-4.1.11.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-19382
Vulnerability Data
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…
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understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 8 hardening rules · 5 OS baselines
V3.2.1V7.4.1V8.3.3V10.3.4
Mitigating Controls (NIST 800-53 r5) AI
Explicit requirement to protect session authenticity structurally prevents the weakness for communications.
SC-24 directly requires the system to fail to a known state that preserves security properties, structurally stopping fallback to a less-secure mode.
SI-17 mandates explicit fail-safe procedures that activate on indicated failures, preventing the insecure fallback behavior.
CP-12 forces entry into a safe mode on detected conditions, limiting exposure but not covering every failure path.
Integrity verification tools detect (but do not stop) the acceptance of data lacking authenticity.
SA-8 requires application of engineering principles that include fail-secure design, reducing the likelihood the weakness is introduced.
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.
Secure-development practices explicitly include designing error and failure handling to remain in a secure state.
CWE-345 directly impairs RC.RP-05's verification of restored-asset integrity/authenticity, largely defeating the outcome while still leaving other restoration-confirmation steps partially viable.
Least-privilege policy and enforcement directly counters the permissive-access fallback example in the CWE.
Hardened baselines and configuration management reduce the chance that error paths default to insecure settings.
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.
Security testing can detect missing or weak data authenticity verification.
Network controls can enforce authenticated channels, reducing risk of accepting unauthentic data.
Secure network services often include authenticity checks for data exchanged over those services.
Cryptographic mechanisms directly verify data origin and integrity, preventing acceptance of unauthentic data.
Secure SDLC incorporates authenticity verification requirements throughout development.
Application security requirements can mandate data authenticity verification mechanisms.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. prevents CWE-345
- V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-345
Oracle Linux 9 (1 rule)
- V-271525 OL 9 must have GPG signature verification enabled for all software repositories. prevents CWE-345
RHEL 7 (2 rules)
- V-204447 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-345
- V-204448 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-345
RHEL 8 (2 rules)
- V-230264 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-345
- V-230265 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. prevents CWE-345
RHEL 9 (1 rule)
- V-257822 RHEL 9 must have GPG signature verification enabled for all software repositories. prevents CWE-345