Vulnerability · Published Mar 19, 2025 · Assigned by GitHub_M
CVE-2025-30144Fast-JWT Improperly Validates iss Claims
Medium 6.5
In plain English
A medium-severity insufficient verification of data authenticity 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 0.6% (higher than 48% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official description
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 5.0.6, the fast-jwt library does not properly validate the iss claim based on the RFC 7519. The iss (issuer) claim validation within the fast-jwt library permits an array of strings as a valid iss value. This design flaw enables a potential attack where a malicious actor crafts a JWT with an iss claim structured as ['https://attacker-domain/', 'https://valid-iss']. Due to the permissive validation, the JWT will be deemed valid. Furthermore, if the application relies on external libraries like get-jwks that do not independently validate the iss claim, the attacker can leverage this vulnerability to forge a JWT that will be accepted by the victim application. Essentially, the attacker can insert their own domain into the iss array, alongside the legitimate issuer, and bypass the intended security checks. This issue is fixed in 5.0.6.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | fast-jwt | 5.0.6 | GHSA-gm45-q3v2-6cf8 |
Affected products (as reported)
Weakness: CWE-345, CWE-290 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
References
- https://github.com/nearform/fast-jwt/security/advisories/GHSA-gm45-q3v2-6cf8 x_refsource_CONFIRM
- https://github.com/nearform/fast-jwt/commit/cc26b1d473f900446ad846f8f0b10eb1c0adcbdd x_refsource_MISC
- https://datatracker.ietf.org/doc/html/rfc7519#page-9 x_refsource_MISC