Detect Rancher Fleet Cross-Namespace Secret Disclosure via Unvalidated valuesFrom References in Elastic Security
CVE-2026-44935 is a critical (CVSS 9.9) authorization bypass vulnerability in Rancher Fleet's Helm Deployer affecting versions 0.12.0-0.12.14, 0.13.0-0.13.10, 0.14.0-0.14.5, and 0.15.0-0.15.1. The Helm Deployer fails to validate namespace boundaries when resolving `valuesFrom` references in GitRepo or Bundle resources, allowing an attacker with access to one namespace to craft a GitRepo or Bundle that references Secrets or ConfigMaps from arbitrary namespaces including cluster-scoped secrets. This constitutes an incorrect authorization check (CWE-863) that can expose credentials, API keys, and sensitive configuration from namespaces the attacker should not have access to. A public PoC is available.
MITRE ATT&CK
- Tactic
- Credential Access Discovery
Elastic Detection Query
sequence by kubernetes.audit.user.username with maxspan=10m
[any where kubernetes.audit.objectRef.resource in ("bundles", "gitrepos") and kubernetes.audit.verb in ("create", "update", "patch") and kubernetes.audit.user.username : "*fleet*"]
[any where kubernetes.audit.objectRef.resource in ("secrets", "configmaps") and kubernetes.audit.verb in ("get", "list") and kubernetes.audit.responseStatus.code == 200
and kubernetes.audit.user.username : "system:serviceaccount:*fleet*"
and kubernetes.audit.objectRef.namespace != kubernetes.audit.user.extra.authentication.kubernetes.io/pod-namespace]EQL sequence query that correlates Bundle or GitRepo creation/update events followed by cross-namespace secret reads from Fleet service accounts within 10 minutes, providing higher-fidelity detection of CVE-2026-44935 exploitation chains.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate Fleet GitRepo deployments that are explicitly authorized to reference secrets in other namespaces
- Fleet upgrades or migrations that temporarily require cross-namespace access during rollout
- Development environments where namespace isolation is intentionally relaxed
Other platforms for CVE-2026-44935
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Fleet valuesFrom Cross-Namespace Secret Read
Expected signal: Kubernetes audit log entry: verb=get, resource=secrets, objectRef.name=victim-secret, objectRef.namespace=fleet-test-victim, user.username=system:serviceaccount:fleet-test-attacker:fleet-*, responseStatus.code=200
- Test 2Enumerate Existing GitRepo valuesFrom Cross-Namespace References
Expected signal: Script output listing cross-namespace references; Kubernetes API audit logs for GET gitrepos and GET bundles at cluster scope
- Test 3Fleet Service Account RBAC Permission Audit for Secret Access
Expected signal: kubectl auth can-i commands generate Kubernetes audit log entries for SubjectAccessReview API calls; RBAC audit output identifies over-privileged Fleet service accounts
- Test 4Monitor Fleet Controller Live for Cross-Namespace Secret Access Events
Expected signal: Real-time stdout alerts for each cross-namespace secret or configmap read event matching Fleet service account patterns
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