CVE-2026-54526: Argo Workflows: Incomplete fix for CVE-2026-31892: ArtifactGC.PodSpecPatch bypass of Strict/Secure templateReferencing

Argo Workflows is an open source container-native workflow engine for orchestrating parallel jobs on Kubernetes. Prior to 3.7.15 and 4.0.6, the allow-list fix for CVE-2026-31892 is incomplete because workflow/util/merge.go ValidateUserOverrides and SanitizeUserWorkflowSpec walk only the top-level fields of WorkflowSpec via reflection, and WorkflowSpec.ArtifactGC is allow-listed wholesale; the struct behind that field, WorkflowLevelArtifactGC, has a PodSpecPatch sub-field whose contents flow unmodified into util.ApplyPodSpecPatch on the artifact-GC pod, the same sink the original fix closed for WorkflowSpec.PodSpecPatch, so a user submitting a Workflow under templateReferencing: Strict or Secure (against a referenced WorkflowTemplate that declares an output artifact and setting spec.artifactGC.strategy: OnWorkflowCompletion) can still inject an arbitrary strategic merge patch into the artifact-GC pod, including hostPath volumes, privileged: true, arbitrary image and command, and hostNetwork: true, defeating the stated purpose of Strict/Secure reference mode. This issue is fixed in versions 3.7.15 and 4.0.6.