Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107719fast-jwt: Verifier cache accepts expired JWTs without iat.

Medium 4.2

In plain English

A medium-severity security flaw 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 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.2Medium

Exploit odds (30 days)0.3%top 80.4% 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 6.3.4, the fast-jwt createVerifier cache can continue accepting a previously valid, signed JWT after its exp time when caching is enabled and the token has exp but no iat. In src/verifier.js, cacheSet derives the exp cache deadline only when iat is present, so the cache falls back to cacheTTL, and a later cache hit returns the saved payload before verifyToken rechecks expiration. An attacker who can replay the same cached bearer token can extend access until the cache entry expires, but cannot forge a token through this issue. This issue is fixed in version 6.3.4.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	fast-jwt	6.3.4	GHSA-x937-hj6v-793p

Affected products (as reported)

Vendor	Product	Versions
nearform	fast-jwt	< 6.3.4

Weakness: CWE-613 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

References

https://github.com/nearform/fast-jwt/security/advisories/GHSA-x937-hj6v-793p x_refsource_CONFIRM
https://github.com/nearform/fast-jwt/commit/fc1ddbbe5ce38066ba2cea0b0ce0233932757167 x_refsource_MISC
https://github.com/nearform/fast-jwt/releases/tag/v6.3.4 x_refsource_MISC