CVE-2024-21652

Executive Summary

CVE-2024-21652 is a critical vulnerability in Argo CD, a declarative GitOps continuous delivery tool for Kubernetes. The flaw allows an attacker to bypass the application's brute force login protection mechanism by chaining a Denial of Service (DoS) vulnerability with an in-memory data storage weakness. This enables unlimited login attempts, significantly increasing the risk of account compromise. The CVSS score is 9.8 (Critical), and the attack vector is network-based with low complexity and no privileges required. The vulnerability affects versions prior to 2.8.13, 2.9.9, and 2.10.4. Patches are available in these versions.

Supply Chain & Package Security

Argo CD is a Go-based application. The vulnerability does not directly affect the Go package ecosystem but impacts the Argo CD server component. Organizations using Argo CD should prioritize patching to prevent brute force attacks and potential account takeovers.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector (AV): Network (N) - The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) - No special conditions or complex attack sequences are required.
• Privileges Required (PR): None (N) - The attacker does not need any authentication or privileges.
• User Interaction (UI): None (N) - No user action is required for exploitation.
• Scope (S): Unchanged (U) - The impact is confined to the vulnerable component.
• Confidentiality (C): High (H) - Successful exploitation could lead to complete disclosure of all resources.
• Integrity (I): High (H) - The attacker can modify any data or files.
• Availability (A): High (H) - The attacker can cause a total shutdown of the affected resource.

Threat Level: Critical. The combination of network exploitability, low complexity, and high impact makes this a severe threat. The ability to bypass brute force protection and perform unlimited login attempts can lead to account takeover and further lateral movement within the Kubernetes cluster.

Deep Dive & Mechanics

The vulnerability is a chain of two weaknesses:

1. Denial of Service (DoS) Flaw: An attacker can send specially crafted requests that cause the Argo CD API server to crash or become unresponsive. This is achieved by exploiting a flaw in how the server handles certain input or session states.

2. In-Memory Data Storage Weakness: Argo CD stores brute force login attempt counters in memory. When the server crashes due to the DoS flaw, this in-memory data is lost. Upon restart, the counters are reset to zero, effectively bypassing the brute force protection mechanism.

Attack Chain:

1. The attacker sends a series of requests that trigger the DoS condition, crashing the Argo CD API server.
2. The server restarts (either automatically or manually), clearing the in-memory brute force counters.
3. The attacker now has a clean slate and can perform unlimited login attempts without triggering rate limiting or account lockout.
4. The attacker can then brute force credentials for any user, including administrators.

This chain can be repeated indefinitely, allowing the attacker to make unlimited login attempts over time.

Vulnerable vs. Patched Code

The vulnerable code is in the authentication and rate-limiting logic of the Argo CD API server. The specific code changes are not publicly detailed, but the patch addresses the following:

• Vulnerable: The brute force protection counters are stored only in memory and are not persisted. A server crash or restart resets these counters.
• Patched: The brute force protection counters are now persisted to a durable storage (e.g., Redis or a database) or the DoS vulnerability is fixed to prevent the crash from occurring. The patch also likely includes input validation to prevent the DoS condition.

Conceptual Code Snippet (Vulnerable):

// Vulnerable: In-memory counter
var loginAttempts = make(map[string]int)

func handleLogin(w http.ResponseWriter, r *http.Request) {
    ip := getClientIP(r)
    loginAttempts[ip]++
    if loginAttempts[ip] > 5 {
        http.Error(w, "Too many requests", http.StatusTooManyRequests)
        return
    }
    // ... authentication logic
}

Conceptual Code Snippet (Patched):

// Patched: Persistent counter using Redis
func handleLogin(w http.ResponseWriter, r *http.Request) {
    ip := getClientIP(r)
    attempts, _ := redisClient.Incr("login_attempts:" + ip)
    if attempts > 5 {
        http.Error(w, "Too many requests", http.StatusTooManyRequests)
        return
    }
    // ... authentication logic
}

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Deploy a vulnerable Argo CD instance (version < 2.8.13) on a Kubernetes cluster.
2. Ensure the Argo CD API server is exposed externally.

Exploitation Steps:

1. Identify Target: Scan for Argo CD instances using Shodan or other reconnaissance tools.
2. Trigger DoS: Send a crafted request to crash the Argo CD API server. This could be a malformed JSON payload or a request that triggers a panic.

   # Example: Sending a malformed request to trigger a crash
   curl -X POST https://target-argocd/api/v1/session -d '{"username":"admin","password":"invalid"}'
   

   (Note: The exact payload to trigger the DoS is not publicly disclosed.)
3. Wait for Restart: Monitor the server status. Once it restarts, the brute force counters are reset.
4. Brute Force: Use a tool like Hydra or a custom script to perform unlimited login attempts.

   # Example using Hydra
   hydra -l admin -P /path/to/passwords.txt https-post-form://target-argocd/api/v1/session:{"username":"^USER^","password":"^PASS^"}:F=Invalid
   

5. Repeat: If the server crashes again, repeat the process to maintain unlimited attempts.

Blue Team (Defensive)

Detection:

1. Monitor for Crashes: Set up alerts for unexpected restarts of the Argo CD API server pod.
2. Rate Limiting: Implement network-level rate limiting (e.g., using a WAF or reverse proxy) to mitigate brute force attempts.
3. Log Analysis: Monitor authentication logs for a high volume of failed login attempts from a single IP address.

Mitigation:

1. Patch Immediately: Upgrade to Argo CD version 2.8.13, 2.9.9, or 2.10.4.
2. Network Segmentation: Restrict access to the Argo CD API server to trusted networks only.
3. Multi-Factor Authentication (MFA): Enforce MFA for all Argo CD users to reduce the risk of credential compromise.

Indicators of Compromise (IOCs)

• Network:
  • High volume of HTTP 401/403 responses from the Argo CD API server.
  • Repeated requests to /api/v1/session with different passwords.
  • Unusual patterns of server crashes and restarts.
• Host:
  • Argo CD API server pod logs showing repeated restarts.
  • System logs indicating out-of-memory (OOM) kills or segmentation faults in the Argo CD process.
• File:
  • No specific file-based IOCs are known.

Detection Engineering

YARA Rule

rule CVE_2024_21652_ArgoCD_BruteForceBypass {
    meta:
        description = "Detects attempts to exploit CVE-2024-21652 in Argo CD logs"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-21652"
    strings:
        $s1 = "Too many requests" nocase
        $s2 = "login_attempts" nocase
        $s3 = "Invalid username or password" nocase
    condition:
        any of ($s1, $s2, $s3)
}

Sigma Rule

title: CVE-2024-21652 Argo CD Brute Force Protection Bypass
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2024-21652 by monitoring for repeated login attempts and server crashes.
author: Valters IT
date: 2024-01-01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-21652
logsource:
    category: application
    product: argo_cd
detection:
    selection:
        - event: "login_failed"
        - event: "server_crash"
    condition: selection
falsepositives:
    - Legitimate high volume of login attempts from a single user
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2024-21652 Argo CD Brute Force Bypass Attempt"; flow:to_server; content:"/api/v1/session"; http_uri; content:"password"; http_client_body; threshold: type both, track by_src, count 10, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Patch: Upgrade to Argo CD version 2.8.13, 2.9.9, or 2.10.4. This is the primary fix.
2. Workaround: If patching is not immediately possible, implement network-level rate limiting and IP whitelisting to restrict access to the Argo CD API server.
3. Monitoring: Enable detailed logging for authentication attempts and server crashes. Set up alerts for anomalies.
4. MFA: Enforce multi-factor authentication for all Argo CD users to reduce the impact of credential compromise.
5. Least Privilege: Ensure that Argo CD service accounts and user accounts have the minimum necessary permissions.

Valters IT

This report is generated for educational and defensive purposes only. Unauthorized exploitation of this vulnerability is illegal.