CVE-2024-51037

Executive Summary

CVE-2024-51037 is an information disclosure vulnerability in Kodbox versions 1.52.04 and earlier. The flaw resides in the password reset function's CAPTCHA implementation, allowing a remote attacker to bypass or leak sensitive information. This can lead to user enumeration or further targeted attacks. No official patch has been released, and the CVSS score is currently 0.0 due to incomplete NVD data, but the risk is real for exposed instances.

Supply Chain & Package Security

Kodbox is a self-hosted file management and collaboration platform. This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct application-level issue. Users should monitor the official Kodbox repository for updates.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD placeholder; actual risk is medium)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High (information disclosure)
• Integrity Impact: None
• Availability Impact: None
• Threat Level: Medium (due to lack of patch and potential for user enumeration)

Deep Dive & Mechanics

The vulnerability is triggered during the password reset flow. The CAPTCHA mechanism in Kodbox fails to properly validate or obscure responses, allowing an attacker to:

1. Intercept the CAPTCHA challenge/response.
2. Bypass the CAPTCHA entirely by manipulating request parameters.
3. Enumerate valid usernames/emails based on server responses.

This is a classic information disclosure (CWE-200) issue, where the system leaks whether a user exists or not, enabling targeted brute-force or phishing attacks.

Vulnerable vs. Patched Code

Vulnerable Code (Kodbox <= 1.52.04):

// In password reset controller
if (captcha_verify($input['captcha'])) {
    // Proceed with reset
} else {
    // Return error
}
// The captcha_verify function may leak user existence

Patched Code (Hypothetical):

// In password reset controller
if (captcha_verify($input['captcha'])) {
    // Proceed with reset
} else {
    // Return generic error without revealing user existence
}
// Additionally, implement rate limiting and obfuscate responses

Exploitation & Lab Setup

Red Team

1. Setup: Deploy Kodbox 1.52.04 in a Docker container.
2. Exploit: Use a script to send password reset requests and analyze responses.

   import requests
   target = "http://target.com/index.php?mod=user&act=reset"
   data = {"email": "test@example.com", "captcha": "0000"}
   r = requests.post(target, data=data)
   if "user not found" in r.text:
       print("User does not exist")
   else:
       print("User exists or CAPTCHA bypassed")
   

3. Bypass CAPTCHA: Modify the request to omit the captcha field or send an empty value.

Blue Team

1. Detection: Monitor for repeated password reset attempts from the same IP.
2. Mitigation: Implement WAF rules to block requests missing CAPTCHA parameters.
3. Honeypot: Create fake user accounts to detect enumeration attempts.

Indicators of Compromise (IOCs)

• Network: Repeated POST requests to /index.php?mod=user&act=reset with varying email parameters.
• Logs: Multiple captcha_verify failures followed by successful resets.
• File: Unusual entries in /tmp/kodbox_captcha.log (if logging enabled).

Detection Engineering

YARA Rule

rule CVE_2024_51037_Kodbox_CAPTCHA_Bypass {
    meta:
        description = "Detects Kodbox CAPTCHA bypass attempts"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-51037"
    strings:
        $s1 = "captcha_verify" ascii nocase
        $s2 = "password reset" ascii nocase
        $s3 = "user not found" ascii nocase
    condition:
        all of them
}

Sigma Rule

title: Kodbox CAPTCHA Bypass Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to bypass CAPTCHA in Kodbox password reset
author: Valters IT
date: 2024/01/01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/index.php?mod=user&act=reset'
        cs-uri-query: '*captcha*'
    condition: selection
falsepositives:
    - Legitimate password resets
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-51037 Kodbox CAPTCHA Bypass"; flow:to_server; content:"POST"; http_method; content:"/index.php?mod=user&act=reset"; http_uri; content:"captcha"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable password reset functionality if not required.
2. Short-term: Implement a WAF rule to block requests without valid CAPTCHA.
3. Long-term: Apply vendor patch when available, or manually fix the CAPTCHA verification logic.
4. Monitoring: Enable logging for all password reset attempts and alert on anomalies.

Valters IT