All Argo CD versions starting with 2.5.0-rc1 are vulnerable to an
authorization bypass bug which allows a malicious Argo CD user to deploy
Applications outside the configured allowed namespaces.

Reconciled Application namespaces are specified as a comma-delimited list
of glob patterns. When sharding is enabled on the Application controller,
it does not enforce that list of patterns when reconciling Applications.
For example, if Application namespaces are configured to be argocd-*, the
Application controller may reconcile an Application installed in a
namespace called other, even though it does not start with argocd-.

Reconciliation of the out-of-bounds Application is only triggered when the
Application is updated, so the attacker must be able to cause an update
operation on the Application resource.
Limitations

This bug only applies to users who have explicitly enabled the
"apps-in-any-namespace" feature by setting application.namespaces in the
argocd-cmd-params-cm ConfigMap or otherwise setting the
--application-namespaces flags on the Application controller and API server
components. The apps-in-any-namespace feature is in beta as of this
Security Advisory's publish date.

The bug is also limited to Argo CD instances where sharding is enabled by
increasing the replicas count for the Application controller.

Finally, the AppProjects' sourceNamespaces field acts as a secondary check
against this exploit. To cause reconciliation of an Application in an
out-of-bounds namespace, an AppProject must be available which permits
Applications in the out-of-bounds namespace.