CVE-2026-35040

const fastJwt = require('fast-jwt'); // Create a verifier with a global regex (stateful modifier) const verify = fastJwt.createVerifier({ key: 'secret', allowedIss: /some-issuer/g // Vulnerable: using /g modifier }); const token = 'valid.token.payload'; // Assume a valid token for some-issuer // First verification attempt try { const payload1 = verify(token); console.log('Attempt 1: Success'); } catch (e) { console.log('Attempt 1: Failed'); } // Second verification attempt (same token) try { const payload2 = verify(token); console.log('Attempt 2: Success'); } catch (e) { console.log('Attempt 2: Failed - Stateful regex caused this'); }

{"cve": {"id": "CVE-2026-35040", "sourceIdentifier": "[email protected]", "published": "2026-04-09T16:16:27.213", "lastModified": "2026-04-17T20:10:05.477", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-440"}, {"lang": "en", "value": "CWE-697"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:*", "versionEndExcluding": "6.2.1", "matchCriteriaId": "2B44A0FB-C037-42E0-9666-7491FF59219D"}]}]}], "references": [{"url": "https://github.com/nearform/fast-jwt/commit/18d25904e4617e8753526d1b3ab5a2cccdea726a", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/nearform/fast-jwt/pull/593", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://github.com/nearform/fast-jwt/releases/tag/v6.2.1", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/nearform/fast-jwt/security/advisories/GHSA-3j8v-cgw4-2g6q", "source": "[email protected]", "tags": ["Exploit", "Mitigation", "Vendor Advisory"]}]}}