Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107720fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set

High 7.4

In plain English

A high-severity improper input validation in fast-jwt from nearform. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.4High

Exploit odds (30 days)0.3%top 74.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	fast-jwt	6.3.1	GHSA-8wpc-h4q6-8fxv

Affected products (as reported)

Vendor	Product	Versions
nearform	fast-jwt	< 6.3.1

Weakness: CWE-20, CWE-347 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References

https://github.com/nearform/fast-jwt/security/advisories/GHSA-8wpc-h4q6-8fxv x_refsource_CONFIRM
https://github.com/nearform/fast-jwt/pull/649 x_refsource_MISC
https://github.com/nearform/fast-jwt/commit/e22a151e83bf6d5e54e281216982d204d5665534 x_refsource_MISC
https://github.com/nearform/fast-jwt/releases/tag/v6.3.1 x_refsource_MISC