CVE-2026-107724 fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
Attackers can forge HS256 tokens by using public JWK JSON as an HMAC secret if HS256 is allowed, bypassing authentication checks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-107724?
CVE-2026-107724 is a high-severity vulnerability in nearform fast-jwt, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-347
Which versions are affected by CVE-2026-107724?
2 open source packages ship an affected version, including fast-jwt.
| Package | Affected | Fixed in |
|---|---|---|
fast-jwt npm | From 6.2.4 | 6.3.0 |
fast-jwt npm | From 6.2.4 | 6.3.0 |
How do I fix CVE-2026-107724?
Upgrade fast-jwt to 6.3.0 or later.
Is CVE-2026-107724 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-107724 exists.
Sources
Also known as GHSA-g3jj-5cmm-3hxx.