GHSA-fhv5-28vv-h8m8
LOWPyJWKClient unbounded JWKS endpoint requests via attacker-controlled kid values (DoS)
Blast Radius
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Description
[!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.
Summary
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.
Impact
- 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)
Suggested Fix
- Add refresh cooldown (refuse refresh more than once per TTL period)
- Move cache write from finally to else block
Affected Versions
All versions with PyJWKClient (2.4.0 through 2.12.1)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | pyjwt | all versions | 2.13.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyjwt. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update pyjwt to 2.13.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fhv5-28vv-h8m8 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-fhv5-28vv-h8m8 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-fhv5-28vv-h8m8. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-fhv5-28vv-h8m8 in your dependencies?
O3 detects GHSA-fhv5-28vv-h8m8 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.