CVE-2026-42541 is a medium-severity (CVSS 4.3) CWE-862 vulnerability in github.com/kubewarden/kubewarden-controller. A fix is available for github.com/kubewarden/kubewarden-controller — see the affected versions and patch details below.
Kubewarden: RBAC Reconnaissance via unchecked can_i host capability call
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 CVE-2026-42541.
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
CVE-2026-42541 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/kubewarden/kubewarden-controllerReal-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
Impact
Kubewarden is a policy engine for Kubernetes. Kubewarden cluster operators can grant permissions to users to deploy namespaced AdmissionPolicies and AdmissionPolicyGroups in their Namespaces. One of Kubewarden promises is that configured users can deploy namespaced policies in a safe manner, without privilege escalation.
An attacker with privileged AdmissionPolicy or AdmissionPolicyGroup create permissions (which isn't the default) can craft a policy that makes use of the can_i host callback. The callback issues a SubjectAccessReview (SAR) requests to enumerate RBAC permissions of any user or service account across the cluster. Three operations on the host capabilities kubewarden/kubernetes binding enforce the context-aware allow-list via can_access_kubernetes_resource():
list_resources_by_namespacelist_resources_allget_resource
However, can_i does not perform that check and forwards the request directly to the callback handler, which executes a real SubjectAccessReview using policy-server privileges. This creates a policy-level authorization gap: can_i is effectively usable even when the policy has no context-aware resource grant.
This is an information disclosure / reconnaissance issue, and not direct workload data exfiltration. The attacker learns permission information, such as whether specific service accounts can "get secrets", "create pods", or "bind clusterroles" in chosen namespaces.
Patches
Cluster Operators, if providing their users with privileges to deploy AdmissionPolicies or AdmissionPolicygroups (which isn't the default), must then also deploy PolicyServers with reduced permissions for host capability calls. This includes the PolicyServer default.
For that, make use of the new feature in v1.35:
- For custom PolicyServers: Set the new
PolicyServer.spec.namespacedPoliciesCapabilities, for example to an empty list[]which doesn't allow any capability. - For the
defaultPolicyServer, set the.Values.policyServer.namespacedPoliciesCapabilities, for example to an empty list[]which doesn't allow any capability.
Also, if needed, they must ensure that those namespaced AdmissionPolicies or AdmissionPolicygroups are scheduled in the PolicyServers with reduced permissions. For that, they could make use of the new ns-policyserver-mapper policy, their own policy or other means, such as GitOps.
See: https://docs.kubewarden.io/howtos/policy-servers/namespaced-policies-capabilities
Workarounds
Cluster Operators can opt for:
- Not allowing users to create namespaced policies (AdmissionPolicies, AdmissionPolicyGroups).
- Removing SubjectAccessReview "create" permissions for the PolicyServer ServiceAccount RBAC being used, in custom PolicyServers and the PolicyServer
default.
Resources
- Code changes, with new security feature: https://github.com/kubewarden/kubewarden-controller/pull/1693
- Documentation changes: https://github.com/kubewarden/docs/pull/737
- Explained new feature on 1.35.0
- Updated Threat model assessment
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/kubewarden/kubewarden-controller | all versions | 1.35.0go get github.com/kubewarden/kubewarden-controller@v1.35.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/kubewarden/kubewarden-controller, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/kubewarden/kubewarden-controller to 1.35.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42541 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 CVE-2026-42541 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42541. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-42541 in your dependencies?
O3 Security finds CVE-2026-42541 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.