Argo Workflows: ArtifactGC.PodSpecPatch bypasses Strict/Secure template reference allow-list (Incomplete fix for CVE-2026-31892)

### Summary The allow-list fix for CVE-2026-31892 (GHSA-3wf5-g532-rcrr), and its follow-up coverage of `hostNetwork`/`securityContext`/`serviceAccountName` in GHSA-3775-99mw-8rp4, is incomplete. `workflow/util/merge.go` `ValidateUserOverrides` / `SanitizeUserWorkflowSpec` walk only the top-level fields of `WorkflowSpec` via reflection. `WorkflowSpec.ArtifactGC` is allow-listed because admins want users to configure artifact garbage collection. 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`. A user submitting a Workflow under `templateReferencing: Strict` or `Secure` can therefore still inject an arbitrary strategic merge patch into the artifact-GC pod (hostPath volumes, `privileged: true`, arbitrary image and command, `hostNetwork: true`), defeating the stated purpose of Strict/Secure reference mode. ### Details Locations in `main` at `4d9f021` (HEAD 2026-04-23): Allow-list and reflection scope - `workflow/util/merge.go:19-60`: ```go var allowedUserOverrideFields = map[string]bool{ "Arguments": true, "Entrypoint": true, ... "ArtifactGC": true, // <-- allow-listed wholesale } func ValidateUserOverrides(userSpec *wfv1.WorkflowSpec) error { v := reflect.ValueOf(userSpec).Elem() t := v.Type() zero := reflect.New(t).Elem() for i := 0; i < t.NumField(); i++ { fieldName := t.Field(i).Name if allowedUserOverrideFields[fieldName] { continue // <-- sub-fields are not walked } if !reflect.DeepEqual(v.Field(i).Interface(), zero.Field(i).Interface()) { violations = append(violations, fieldName) } } ... } ``` The allow-listed type - `pkg/apis/workflow/v1alpha1/workflow_types.go:1207-1217`: ```go type WorkflowLevelArtifactGC struct { ArtifactGC `json:",inline"` ForceFinalizerRemoval bool `json:"forceFinalizerRemoval,omitempty"` PodSpecPatch string `json:"podSpecPatch,omitempty"` // <-- sink input } ``` The sink - `workflow/controller/artifact_gc.go:731-740` reads the user-controlled value: ```go func (woc *wfOperationCtx) getArtifactGCPodInfo(artifact *wfv1.Artifact) podInfo { info := podInfo{} if woc.execWf.Spec.ArtifactGC != nil { woc.updateArtifactGCPodInfo(&woc.execWf.Spec.ArtifactGC.ArtifactGC, &info) info.podSpecPatch = woc.execWf.Spec.ArtifactGC.PodSpecPatch } ... } ``` And `workflow/controller/artifact_gc.go:518-525` feeds it unchanged to the same helper that CVE-2026-31892 closed for the top-level field: ```go if info.podSpecPatch != "" { patchedPodSpec, patchErr := util.ApplyPodSpecPatch(pod.Spec, info.podSpecPatch) if patchErr != nil { return nil, patchErr } pod.Spec = *patchedPodSpec } ``` `util.ApplyPodSpecPatch` (`workflow/util/util.go:1560`) is a raw `strategicpatch.StrategicMergePatch` over the whole `apiv1.PodSpec` with no field-level restriction; it is the same primitive that was weaponized by the original CVE-2026-31892 against `WorkflowSpec.PodSpecPatch`. The pod it is applied to - built in `workflow/controller/artifact_gc.go` ~line 460-495 - has `AutomountServiceAccountToken: true` and a hardened `MinimalCtrSC()` security context that the patch fully overrides. The merge path is the one the fix already walks. `operator.go:#setStoredWfSpec` does `SanitizeUserWorkflowSpec(&woc.wf.Spec)` before `JoinWorkflowSpec(userSpec, workflowTemplateSpec, wfDefaultSpec)`. `Sanitize` preserves `ArtifactGC` wholesale. `Join` uses `strategicpatch.StrategicMergePatch` with the user spec as the target, so the user's `artifactGC.podSpecPatch` value wins whenever it is non-empty. Precondition for the attack: the referenced `WorkflowTemplate` has at least one template with an output artifact

CVSS 4.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-284

Also known as

BIT-argo-workflows-2026-54526, CVE-2026-54526, GO-2026-6223

• github.com/argoproj/argo-workflows/security/advisories/GHSA-48p8-g2fx-3wwm
• nvd.nist.gov/vuln/detail/CVE-2026-54526
• github.com/argoproj/argo-workflows/commit/277e9cef0ad16d7eaaab253573d0695951a65dbd
• github.com/argoproj/argo-workflows/commit/358cc3968c8f06f1be0967e41df191088db0b662
• github.com/argoproj/argo-workflows
• github.com/argoproj/argo-workflows/releases/tag/v3.7.15
• github.com/argoproj/argo-workflows/releases/tag/v4.0.6