fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
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| nearform | fast-jwt | affected |
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| Nearform | Fast-jwt |
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| Source | ID | Title |
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Github GHSA |
GHSA-ww5h-9m49-7xx4 | fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion |
No CVSS v4.0
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.356% probability within 30 days)
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| Metrics |
ssvc
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| First Time appeared |
Nearform
Nearform fast-jwt |
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| Vendors & Products |
Nearform
Nearform fast-jwt |
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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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