CVE-2026-107720 fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set
Attackers can bypass authentication by submitting unsigned JWTs when the verifier is configured with an empty key and explicit algorithms.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-107720?
CVE-2026-107720 is a high-severity authentication bypass 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. Prior to 6.3.1, fast-jwt createVerifier accepts an unsigned JWT when key is an empty string or null and algorithms is a non-empty allowlist. Falsy synchronous keys bypass prepareKeyOrSecret, allowedAlgorithms remains active, hasKey is false, and the empty signature avoids the verifySignature gate. An attacker can therefore submit a token containing arbitrary claims without possessing a signing key, resulting in authentication or authorization bypass. Claim validators still run, and non-empty keys, an empty key without algorithms, and the async key resolver path do not have this behavior. This issue is fixed in version 6.3.1.
Which versions are affected by CVE-2026-107720?
2 open source packages ship an affected version, including fast-jwt.
| Package | Affected | Fixed in |
|---|---|---|
fast-jwt npm | All versions | 6.3.1 |
fast-jwt npm | All versions | 6.3.1 |
How do I fix CVE-2026-107720?
Upgrade fast-jwt to 6.3.1 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-107720 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-107720 exists.
Sources
Also known as GHSA-8wpc-h4q6-8fxv.