CVE-2026-107724
published 2026-10-08CVE-2026-107724: fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because…
PriorityP347high7.4CVSS 3.1
AVNACHPRNUINSUCHIHAN
EPSS
0.22%
12.1th percentile
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.2.4, fast-jwt can classify raw serialized public JWK or JWKS JSON as an HMAC secret because src/crypto.js performDetectPublicKeyAlgorithms treats non-PEM strings as symmetric key material. If HS256 is explicitly allowed or inferred, an attacker who knows the exact serialized public-key bytes can use those bytes as an HMAC key and create a token containing arbitrary claims that createVerifier accepts. Serialization ordering or whitespace differences can prevent exploitation, and applications using supported PEM keys with an asymmetric-only algorithm allowlist are not affected. This issue is fixed in version 6.3.0.
Affected
2 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| nearform | fast-jwt | — | — |
| nearform | fast-jwt | >= 6.2.4 < 6.3.0 | 6.3.0 |
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VulDB
nearform fast-jwt up to 6.2.x Key Algorithm Detection src/crypto.js performDetectPublicKeyAlgorithms deserialization
vuldb·2026-10-09·CVSS 7.4
CVE-2026-107724 [HIGH] nearform fast-jwt up to 6.2.x Key Algorithm Detection src/crypto.js performDetectPublicKeyAlgorithms deserialization
A vulnerability was found in nearform fast-jwt up to 6.2.x. It has been declared as critical. This vulnerability affects the function performDetectPublicKeyAlgorithms of the file src/crypto.js of the component Key Algorithm Detection. The manipulation results in deserialization.
This vulnerability was named CVE-2026-107724. The attack may be performed from remote. There is no available exploit.
It is recommended to upgrade the affected component.
GHSA
fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
ghsa·2026-10-08
CVE-2026-107724 [HIGH] CWE-347 fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
### Summary
`fast-jwt` 6.2.4 silently classifies raw serialized public JWK JSON
as an HMAC secret.
If an application supplies public JWK JSON text as the verifier key and
HS256 is explicitly allowed or automatically inferred, an attacker who
knows the same public JSON text can use it as an HMAC key and create an
arbitrary HS256 token that `fast-jwt` accepts as valid.
This can result in authentication or authorization bypass through forged
JWT claims.
The PoC demonstrates the issue with a serialized RSA public JWK. The same
non-PEM classification also applies to raw JWKS JSON text, although the
attached standalone PoC focuses on the smallest JWK case.
### Details
The verifier accepts a string or Buffe
No detection rules found.
No public exploits indexed.
No writeups or analysis indexed.
https://github.com/nearform/fast-jwt/commit/10f9591349199ed2ab9fa1748ce92cdca697f6cfhttps://github.com/nearform/fast-jwt/pull/636https://github.com/nearform/fast-jwt/releases/tag/v6.3.0https://github.com/nearform/fast-jwt/security/advisories/GHSA-g3jj-5cmm-3hxxhttps://github.com/nearform/fast-jwt/security/advisories/GHSA-g3jj-5cmm-3hxx
2026-10-08
Published