Rancher Fleet vulnerable to cross namespace secret disclosure via unvalidated `valuesFrom` references in Helm Deployer

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 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 require a specific service account for the Fleet agent on downstream clusters used for deployment. The agent uses these designated service accounts for operations, blocking access to unauthorized resources.
• Restrict HelmOp repository and chart URLs by using a regular expression. The regular expression is automatically anchored with ^ and $, meaning it must match the entire URL string.

Like GitRepoRestriction, a Policy resource must be created in the specific namespace you want to restrict, and it only applies to that namespace.