GHSA-3j3q-wp9x-585p — kcp
HIGHGHSA-3j3q-wp9x-585p is a high-severity (CVSS 8.2) CWE-302 vulnerability in github.com/kcp-dev/kcp. A fix is available for github.com/kcp-dev/kcp — see the affected versions and patch details below.
kcp's cache server is accessible without authentication or authorization checks
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3j3q-wp9x-585p.
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.
How urgent is this, really
GHSA-3j3q-wp9x-585p plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/kcp-dev/kcp🐹github.com/kcp-dev/kcpReal-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
Summary
The cache server is directly exposed by the root shard and has no authentication or authorization in place. This allows anyone who can access the root shard to read and write to the cache server.
Details
The cache server is routed in the pre-mux chain in the shard code. The preHandlerChainMux is handled before any authn/authz in the cache server: https://github.com/kcp-dev/kcp/blob/aaf93d59cbcd0cefb70d94bd8959ce390547c4a2/pkg/server/config.go#L514-L518
This results in the cache server being proxied before any authn/authz in the handler chain takes place.
Attack Vectors
1. Unauthenticated Read Access (Primary)
An attacker can read all replicated resources from the cache without any credentials. This exposes:
| Category | Resources | Severity | Reason |
|---|---|---|---|
| RBAC | clusterroles, clusterrolebindings (filtered by annotation) | High | Only subset with internal.kcp.io/replicate annotation: access rules, APIExport bind/content rules, WorkspaceType use rules. Reveals permission structure for API access and tenancy. Roles/RoleBindings NOT replicated. |
| Infrastructure | logicalclusters, shards | High | Reveals full cluster topology and shard configuration |
| API surface | apiexports, apiexportendpointslices, apiresourceschemas | High | Reveals all exported APIs and their network endpoints |
| Admission control | mutatingwebhookconfigurations, validatingwebhookconfigurations, validatingadmissionpolicies | High | Reveals admission policies, aids bypass |
| Tenancy | workspacetypes | Medium | Reveals workspace structure |
| Cache metadata | cachedobjects, cachedresources, cachedresourceendpointslices | Medium | Exposes cache state and resource endpoints |
2. Write Access with Race Condition (Secondary)
The cache server allows full CRUD operations. While injected objects are cleaned up by the replication controller, a race condition exists that could allow temporary privilege escalation.
The race window:
- Attacker POSTs a malicious ClusterRole + ClusterRoleBinding to the cache server
- Cache etcd watch fires and notifies two consumers in parallel: 2.1. The authorization informer (CacheKubeSharedInformerFactory) updates its in-memory store — the GlobalAuthorizer and WorkspaceContentAuthorizer now see the injected RBAC rules 2.2. The replication controller's informer enqueues a reconcile to its workqueue
- Replication controller worker dequeues, calls getLocalCopy() → not found, deletes the object
Between steps 2 and 3, any API request hitting the GlobalAuthorizer (global_authorizer.go:89-101) would evaluate RBAC against a store that includes the attacker's injected rules. The authorization informer and the replication controller share the same CacheKubeSharedInformerFactory (config.go:361), so the object is visible to authorization as soon as the informer cache updates — before the replication controller can process and delete it.
Practical exploitability is low — the window is sub-second, requiring the attacker to fire the privileged API request with precise timing. However, it could be automated in a tight loop. The workqueue rate limiter could also widen the window under load.
Self-healing mechanism: The replication controller acts as a self-healing mechanism. Objects injected into the cache are deleted almost instantly because:
Creating an object in cache triggers the cache informer Replication controller reconciles, calls getLocalCopy() → not found Controller calls deleteObject() on the cache copy (replication_reconcile.go:157-168)
Replicatable
Start a kcp root shard and query the cache server, e.g. with:
curl --insecure 'https://root.vespucci.genericcontrolplane.io:6443/services/cache/shards/root/clusters/root/apis/apis.kcp.io/v1alpha1'
Workarounds
Network-level access control: Restrict access to /services/cache/* paths at the load balancer, reverse proxy, or firewall level. External cache server: Deploy the cache server separately with its own kubeconfig (--cache-server-kubeconfig) and restrict network access to it.
Impact
Who is affected: Any kcp deployment where the root shard is network-reachable by untrusted clients. This applies when:
- Helm chart deployments: Affected if the shard's Service or Ingress exposes port 6443 externally.
- Operator deployments: Affected if the Shard resource has spec.externalURL set (or spec.baseURL — externalURL defaults to baseURL if unset). When a shard has an external URL, clients route to it directly, exposing the /services/cache/* path.
- Any deployment method: If the root shard's --shard-external-url is set and reachable from untrusted networks, the cache server is exposed.
Not affected: Deployments where the root shard is behind a front-proxy and is not directly reachable. The front-proxy does not forward /services/cache/* requests.
Write persistence: The replication controller watches the cache informer and acts as a self-healing mechanism. Objects injected into the cache are deleted almost instantly (sub-second) because:
- Creating an object in cache triggers the cache informer
- Replication controller reconciles, calls getLocalCopy() → not found
- Controller calls deleteObject() on the cache copy (replication_reconcile.go:157-168)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/kcp-dev/kcp | ≥ 0.30.0&&< 0.30.3 | 0.30.3go get github.com/kcp-dev/kcp@v0.30.3 |
| 🐹Go | github.com/kcp-dev/kcp | all versions | 0.29.3go get github.com/kcp-dev/kcp@v0.29.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/kcp-dev/kcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/kcp-dev/kcp to 0.30.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3j3q-wp9x-585p 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-3j3q-wp9x-585p can be triaged on real exposure rather than presence alone.
Tailored to GHSA-3j3q-wp9x-585p. 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-3j3q-wp9x-585p in your dependencies?
O3 Security finds GHSA-3j3q-wp9x-585p across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.