CVE-2026-48524

[!NOTE]
The vulnerability surfaces only when a JWKS fetch fails; an attacker can attempt to provoke that with sustained unknown-kid traffic, but the outcome depends on upstream JWKS-endpoint behavior (rate limiting, transient errors) which is beyond the attacker's control. Impact is reduced auth availability until the next successful fetch, not complete denial of service.

PyJWKClient.get_signing_key() forces a fresh HTTP request to the JWKS endpoint for every JWT with an unknown kid value, with no rate limiting. Since kid comes from the unverified token header, an attacker can trigger unlimited outbound requests.

Additionally, fetch_data() finally block clears the JWKS cache on network error.

Root Cause

jwt/jwks_client.py:172-198 - get_signing_key(kid) calls get_signing_keys(refresh=True) for unknown kids, bypassing TTL cache with no cooldown.
jwt/jwks_client.py:120-122 - finally block writes None to cache on error, clearing valid data.

Affected Versions

All versions with PyJWKClient (2.4.0 through 2.12.1)

• DoS against JWKS endpoint (unlimited requests per invalid token)
• DoS against application (network I/O latency)
• Cascading failure (rate limiting clears cache, breaking legitimate auth)

CVE-2026-48524 has a CVSS score of 3.7 (Low). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.13.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. Add refresh cooldown (refuse refresh more than once per TTL period)
2. Move cache write from finally to else block

1. What is CVE-2026-48524? CVE-2026-48524 is a low-severity security vulnerability in pyjwt (pip), affecting versions <= 2.12.1. It is fixed in 2.13.0.
2. How severe is CVE-2026-48524? CVE-2026-48524 has a CVSS score of 3.7 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of pyjwt are affected by CVE-2026-48524? pyjwt (pip) versions <= 2.12.1 is affected.
4. Is there a fix for CVE-2026-48524? Yes. CVE-2026-48524 is fixed in 2.13.0. Upgrade to this version or later.
5. Is CVE-2026-48524 exploitable, and should I be worried? Whether CVE-2026-48524 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-48524 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-48524? Upgrade pyjwt to 2.13.0 or later.