fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4.
Metrics
Affected Vendors & Products
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History
Thu, 14 May 2026 19:15:00 +0000
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ssvc
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Wed, 13 May 2026 22:00:00 +0000
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Nearform
Nearform fast-jwt |
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Nearform
Nearform fast-jwt |
Wed, 13 May 2026 20:00:00 +0000
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| Description | fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4. | |
| Title | fast-jwt: Empty HMAC secret accepted via async key resolver - JWT auth bypass | |
| Weaknesses | CWE-1391 CWE-287 CWE-326 |
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cvssV3_1
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Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-05-14T18:13:32.626Z
Reserved: 2026-05-05T19:52:59.148Z
Link: CVE-2026-44351
Updated: 2026-05-14T18:13:23.007Z
Status : Deferred
Published: 2026-05-13T20:16:22.860
Modified: 2026-05-14T19:16:37.050
Link: CVE-2026-44351
No data.
OpenCVE Enrichment
Updated: 2026-05-13T22:15:09Z