Critical, CVSS 9.4npmAmendedPublished
get-jwks: poisoned JWKS cache allows post-fetch issuer validation bypass
CVE-2025-59936 · GHSA-qc2q-qhf3-235m
- Affected
- npm get-jwks <= 11.0.1
- Fixed in
- 11.0.2· Vendor fix available
- Issue
- A vulnerability in get-jwks can lead to cache poisoning in the JWKS key-fetching mechanism. Details When the iss (issuer) claim is validated only after keys are retrieved from the cache, it is possible for cached keys from an unexpected issuer to be reused, resulting in a bypass of issuer validation. This design flaw enables a potential attack where a malicious actor crafts a pair of JWTs, the first one ensuring that a chosen public key is fetched and stored in the shared JWKS cache, and the second one leveraging that cached key to pass signature validation for a targeted iss value. The vulnerability will work only if the iss validation is done after the use of get-jwks for keys retrieval, which usually is the common case. PoC Server code: Exploit server that generates the JWT pair and send the public RSA key to the victim server: The first JWT token will create a cache entry with the chosen public key and have the following format:…
Recommended action: Upgrade to 11.0.2 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.