Argo Vulnerable to Unauthenticated Memory Exhaustion (DoS) in Webhook Interceptor

Overview

Severity: Medium Component: Webhook Interceptor (server/auth/webhook) Vulnerability Type: Denial of Service (DoS)

Description

The Webhook Interceptor loads the entire request body into memory before authenticating the request or verifying its signature. This occurs on the /api/v1/events/ endpoint, which is publicly accessible (albeit intended for webhooks). An attacker can send a request with an extremely large body (e.g., multiple gigabytes), causing the Argo Server to allocate excessive memory, potentially leading to an Out-Of-Memory (OOM) crash and denial of service.

Vulnerable Code

In server/auth/webhook/interceptor.go:

func (i *WebhookInterceptor) addWebhookAuthorization(r *http.Request, kube kubernetes.Interface) error {
    // ... basic checks ...
    
    // Vulnerability: Reads entire body into memory unconditionally
    buf, _ := io.ReadAll(r.Body)
    defer func() { r.Body = io.NopCloser(bytes.NewBuffer(buf)) }()
    
    // ... subsequent logic finds correct service account and secret ...
    // ... verification happens later ...
}

The io.ReadAll call happens before the signature verification loop.

Impact

• Service Availability: An attacker can crash the Argo Server, disrupting workflow execution and API access for all users.

PoC (Conceptual)

1. Target the webhook endpoint: POST /api/v1/events/some-namespace
2. Send a Content-Length: 1000000000 (1GB) header.
3. Stream 1GB of random data.
4. Monitor server memory usage. It will spike until 1GB is allocated or the process crashes.

Recommendation

1. Limit Body Size: Enforce a strict limit on webhook body size (e.g., 10MB) using http.MaxBytesReader.
2. Streaming Verification: If possible, verify the signature in a streaming fashion or use a temporary file for large payloads (though typically webhooks are small).

Affected packages

• github.com/argoproj/argo-workflows/v3 < 3.7.14
• github.com/argoproj/argo-workflows/v4 >= 4.0.0, < 4.0.5

Remediation

Upgrade to a patched release:

• github.com/argoproj/argo-workflows/v3 3.7.14
• github.com/argoproj/argo-workflows/v4 4.0.5