CVE-2025-59936: get-jwks: poisoned JWKS cache allows post-fetch issuer validation bypass

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 33: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 33% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes get-jwks (npm) <= 11.0.1, fixed in 11.0.2. Check your lockfile, including transitive dependencies.

What it is

get-jwks contains fetch utils for JWKS keys. In versions prior to 11.0.2, a vulnerability in get-jwks can lead to cache poisoning in the JWKS key-fetching mechanism. 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. This issue has been patched in version 11.0.2.

From the GitHub advisory

Summary 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:

Weakness type: CWE-116.

Product: get-jwks (npm) · Assigned by: GitHub_M · Published: 2025-09-27

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.40% probability of exploitation activity in the next 30 days; percentile 33.

Timeline

• 2025-09-26 — GitHub-reviewed advisory GHSA-qc2q-qhf3-235m published (critical)
• 2025-09-27 — CVE record published by GitHub_M
• 2025-09-29 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-qc2q-qhf3-235m github.com
2. CVE.org record CVE-2025-59936 cve.org
3. NVD entry CVE-2025-59936 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

Critical npm advisories · Today’s Security Digest