Detect Rancher Fleet Cross-Namespace Secret Disclosure via Unvalidated valuesFrom References in Google Chronicle
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
YARA-L Detection Query
rule rancher_fleet_cve_2026_44935_cross_namespace_secret_read {
meta:
author = "df00tech"
description = "Detects Rancher Fleet cross-namespace secret disclosure CVE-2026-44935"
severity = "CRITICAL"
priority = "HIGH"
reference = "https://github.com/rancher/fleet/security/advisories/GHSA-xr65-5cpm-g36x"
events:
$e.metadata.event_type = "USER_RESOURCE_ACCESS"
$e.target.resource.type = "KUBERNETES_OBJECT"
$e.target.resource.resource_subtype in ("secrets", "configmaps")
$e.network.http.method in ("GET", "LIST")
$e.principal.user.userid matches /system:serviceaccount:.*fleet.*/
$e.network.http.response_code = 200
$source_ns = re.capture($e.principal.user.userid, "system:serviceaccount:([^:]+):")
$e.target.namespace != $source_ns
$e.target.namespace != ""
match:
$e.principal.user.userid over 5m
outcome:
$risk_score = 85
$target_namespace = $e.target.namespace
$source_namespace = $source_ns
$secret_name = $e.target.resource.name
condition:
$e
}Chronicle YARA-L rule detecting Rancher Fleet service accounts successfully reading secrets or configmaps from namespaces different from their own, indicating exploitation of CVE-2026-44935.
Data Sources
Required Tables
False Positives & Tuning
- Authorized cross-namespace Fleet configurations in clusters with relaxed multi-tenancy controls
- Fleet upgrade procedures that require temporary elevated secret access across namespaces
- GKE Autopilot or Workload Identity configurations where Fleet service accounts are granted broader permissions
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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