Rancher Fleet vulnerable to cross namespace secret disclosure via unvalidated `valuesFrom` references in Helm Deployer
Date: 2026-07
Affected: go/github.com/rancher/fleet, go/github.com/rancher/fleet, go/github.com/rancher/fleet
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: Critical
CVE: CVE-2026-44935
CWE: CWE-863
CVSS: 9.9 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H)

### Impact A vulnerability in Fleet for Rancher Manager affects multi-tenancy environments where different tenants share the same downstream clusters (e.g., different privileged or untrusted teams inside the same organization). On unpatched versions, tenants could bypass restrictions to access any config map or secret across all namespaces on the downstream cluster. They can create cluster-wide resources using `HelmOp` or `Bundle` without authorization. Specifically, an attacker can exploit this vulnerability in the following ways: 1. Use `valuesFrom` in `fleet.yaml`(through a `GitRepo` resource) or a `HelmOp resource to read the contents of any secret an on the downstream cluster, provided they know or can guess the name, namespace, and key. 2. Deploy `HelmOp` and `Bundle` resources without being restricted to a specific service account for the Fleet agent. If you use Fleet in a multi-tenant environment, it's recommended that you: - Review your cluster and Fleet deployments logs for indicators of unauthorized access across tenant namespaces. - Rotate any service accounts and credentials that might have been exposed. Please consult the associated [MITRE ATT&CK - Technique - Unsecured Credentials](https://attack.mitre.org/techniques/T1552/) for further information about this category of attack. ### Patches To resolve this vulnerability, upgrade to a patched version of Fleet. The new Policy resource allows you to: - Configure `GitRepos`, `HelmOps`, and `Bundles` to requi


Mitigations:

Architectural layers (MAESTRO):