CVE-2026-107723 fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array
Attackers can bypass JWT claim validations like expiry and issuer by using a JSON array payload, affecting applications using fast-jwt.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-107723?
CVE-2026-107723 is a high-severity vulnerability in nearform fast-jwt, published on 8 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts a validly signed JWT whose payload is a JSON array because src/decoder.js checks that the payload is an object but does not reject arrays. The claim validator loop then finds no named exp, nbf, iss, aud, sub, jti, or nonce properties and silently skips those configured checks, returning the array as a successfully verified payload. An attacker who can produce or influence a validly signed token may bypass expiry, issuer, audience, subject, revocation, and replay protections. The opt-in requiredClaims option can block missing claims, and signature verification itself is not bypassed. This issue is fixed in version 6.3.0.
Weakness: CWE-1287
Which versions are affected by CVE-2026-107723?
2 open source packages ship an affected version, including fast-jwt.
| Package | Affected | Fixed in |
|---|---|---|
fast-jwt npm | All versions | 6.3.0 |
fast-jwt npm | All versions | 6.3.0 |
How do I fix CVE-2026-107723?
Upgrade fast-jwt to 6.3.0 or later.
Is CVE-2026-107723 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-107723 exists.
Sources
Also known as GHSA-5hjw-83fp-phq9.