fast-jwt provides fast JSON Web Token (JWT) implementation. From 6.2.0 until 6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the key has non-whitespace content before its PEM header. In src/crypto.js, performDetectPublicKeyAlgorithms trims whitespace but publicKeyPemMatcher remains start-anchored, so comments, control characters, zero-width characters, or wrapper text can prevent PEM detection and reach the HMAC fallback. An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass. An asymmetric-only algorithm allowlist prevents the attack. This issue is fixed in version 6.3.0.
Metrics
Affected Vendors & Products
References
History
Tue, 13 Oct 2026 17:30:00 +0000
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ssvc
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Fri, 09 Oct 2026 00:15:00 +0000
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Nearform
Nearform fast-jwt |
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Nearform
Nearform fast-jwt |
Thu, 08 Oct 2026 22:00:00 +0000
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| Description | fast-jwt provides fast JSON Web Token (JWT) implementation. From 6.2.0 until 6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the key has non-whitespace content before its PEM header. In src/crypto.js, performDetectPublicKeyAlgorithms trims whitespace but publicKeyPemMatcher remains start-anchored, so comments, control characters, zero-width characters, or wrapper text can prevent PEM detection and reach the HMAC fallback. An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass. An asymmetric-only algorithm allowlist prevents the attack. This issue is fixed in version 6.3.0. | |
| Title | fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion | |
| Weaknesses | CWE-347 | |
| References |
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| Metrics |
cvssV3_1
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Status: PUBLISHED
Assigner: GitHub_M
Published: 2026-10-08T21:49:55.888Z
Updated: 2026-10-13T16:26:25.790Z
Reserved: 2026-10-08T17:21:52.975Z
Link: CVE-2026-107722
Updated: 2026-10-13T16:26:21.743Z
Status : Deferred
Published: 2026-10-08T22:17:28.447
Modified: 2026-10-13T17:17:16.970
Link: CVE-2026-107722
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