GHSA-p4gq-3vxj-f4jq: Argo Affected by SSO RBAC Delegation Nil Pointer Dereference DoS (gatekeeper.go)

A nil pointer dereference (accessing data at a null memory address) in Argo Workflows v4.0.4 causes the server to crash with an HTTP 500 error for SSO (single sign-on) users when RBAC delegation (role-based access control rules delegated to namespaces) is enabled. This happens specifically when a user's SSO claims match a namespace-level RBAC rule but not an SSO-namespace rule, causing a permanent denial of service (inability to use the system) for affected users.