Rancher's External RoleTemplates can lead to privilege escalation

Impact

A vulnerability has been identified whereby privilege escalation checks are not properly enforced for RoleTemplateobjects when external=true, which in specific scenarios can lead to privilege escalation.

The bug in the webhook rule resolver ignores rules from a ClusterRole for external RoleTemplates when its context is set to either project or is left empty. The fix introduces a new field to the RoleTemplate CRD named ExternalRules. The new field will be used to resolve rules directly from the RoleTemplate. Additionally, rules from the backing ClusterRole will be used if ExternalRules is not provided. The new field will always take precedence when it is set, and serve as the source of truth for rules used when creating Rancher resources on the local cluster.

Please note that this is a breaking change for external RoleTemplates, when context is set to project or empty and the backing ClusterRole does not exist, as this was not previously required.

Important: The fix is automatically applied when upgrading to the release lines 2.8and above. For users still on the 2.7 release line, after the upgrade to a patched version, users are required to opt-in to the fix by enabling the external-rules feature flag.

Please consult the associated MITRE ATT&CK - Technique - Exploitation for Privilege Escalation for further information about this category of attack.

Patches

Patched versions include releases 2.7.14 and 2.8.5.

Workarounds

The following script was developed for Rancher Manager administrators to identify RoleTemplates impacted by this vulnerability. The script requires jq installed and a kubeconfig with access to Rancher local cluster; it can also be executed in Rancher’s kubectl shell.

#!/bin/bash
set -euo pipefail

# get all RoleTemplates with .context == "project" or .context == "" that don't have externalRules.
rts=$(kubectl get roletemplates -o json | jq -r  '.items[] | select((.context == "project" or .context == "") and .external == true and .externalRules == null and .builtin == false) | .metadata.name')
found_invalid_rt=false

for rt in $rts; do
  if ! kubectl get clusterrole "$rt" > /dev/null 2>&1; then
     echo "$rt" # prints RoleTemplate names that don't have a backing ClusterRole
     found_invalid_rt=true
  fi
done

if ! $found_invalid_rt ; then
    echo 'This cluster is not affected by CVE-2023-32197: no RoleTemplate objects found'
fi

It will return all objects affected by this vulnerability. The administrator can fix those objects by creating the backing ClusterRole that they refer to.

References

• CVE-2023-32196

If you have any questions or comments about this advisory:

• Reach out to the SUSE Rancher Security team for security-related inquiries.
• Open an issue in the Rancher repository.
• Verify with our support matrix and product support lifecycle.