How to remediate – PHP Topsites counter.php count_log_file Parameter Arbitrary Fi…

1. Introduction

The PHP Topsites counter.php count_log_file Parameter Arbitrary File Overwrite vulnerability affects web applications using the ‘counter.php’ CGI script. This flaw allows an attacker to overwrite files on the server, potentially leading to remote code execution or data compromise. Systems running vulnerable versions of this CGI are at risk. A successful exploit could result in loss of confidentiality, integrity and availability of affected systems.

2. Technical Explanation

The counter.php script does not properly sanitise user-supplied input for the ‘count_log_file’ parameter. This allows an attacker to specify a path to overwrite arbitrary files on the system with the privileges of the web server user. Exploitation requires network access to the vulnerable CGI script. There is no known CVE associated with this specific vulnerability, but similar flaws are tracked under CWE-59 (Improper Input Validation). An example attack involves sending a crafted HTTP request containing a malicious ‘count_log_file’ parameter pointing to a sensitive system file.

• Root cause: Missing input validation on the ‘count_log_file’ parameter allows path traversal.
• Exploit mechanism: An attacker sends an HTTP request with a manipulated ‘count_log_file’ value, specifying a target file for overwriting. For example, using “/etc/passwd” as the count_log_file could overwrite system credentials.
• Scope: Web servers running PHP and utilising the counter.php CGI script are affected. Specific versions were not provided in the context.

3. Detection and Assessment

Confirming vulnerability involves checking for the presence of the vulnerable script and verifying its configuration. A thorough assessment requires reviewing source code or network traffic.

• Quick checks: List files on the web server to identify counter.php. Use a command like ls -l /path/to/webroot/counter.php.
• Scanning: Nessus plugin ID 10423 may detect this vulnerability, but results should be verified manually.
• Logs and evidence: Web server access logs may show requests to counter.php with suspicious ‘count_log_file’ parameters. Check for unusual file write activity in system logs.

ls -l /var/www/html/counter.php

4. Solution / Remediation Steps

The recommended solution is to remove the vulnerable CGI script from the web server.

4.1 Preparation

• Ensure you have access to restore the backup in case of issues. A roll back plan involves restoring the backed-up files and restarting the webserver.
• A change window may be required depending on your organisation’s policies, with approval from a senior administrator.

4.2 Implementation

1. Step 1: Remove the counter.php file from the web server directory using the command rm /path/to/webroot/counter.php.
2. Step 2: Verify that the file has been deleted using the command ls -l /path/to/webroot/counter.php (this should return an error).
3. Step 3: Restart the web server service to apply the changes. For Apache, use systemctl restart apache2.

4.3 Config or Code Example

Before

# counter.php exists in webroot directory

After

# counter.php does not exist in webroot directory

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of vulnerability.

• Practice 1: Least privilege – run the web server process with minimal necessary permissions to limit potential damage from exploitation.

4.5 Automation (Optional)

#!/bin/bash
# Script to remove counter.php from all web directories
for dir in /var/www/*; do
  if [ -f "$dir/counter.php" ]; then
    echo "Removing counter.php from $dir"
    rm "$dir/counter.php"
  fi
done
# Caution: This script removes files without confirmation. Test thoroughly before use.

5. Verification / Validation

Confirm the fix by verifying that the file has been removed and attempting to access it.

• Post-fix check: Run ls -l /path/to/webroot/counter.php, which should return an error indicating the file does not exist.
• Re-test: Repeat the initial detection method (listing files) to confirm counter.php is no longer present.
• Monitoring: Monitor web server access logs for any attempts to access counter.php, which should now result in 404 errors.

ls -l /var/www/html/counter.php

6. Preventive Measures and Monitoring

Implement security baselines and automated checks to prevent similar vulnerabilities.

• Baselines: Update your web server security baseline to prohibit the use of outdated or vulnerable CGI scripts like counter.php.
• Asset and patch process: Regularly review installed software and apply security patches promptly. A monthly review cycle is recommended.

7. Risks, Side Effects, and Roll Back

Removing counter.php may disrupt any functionality that relies on it.

• Roll back: Restore the backed-up web application directory and restart the web server service.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory was provided in the context.
• NVD or CVE entry: No specific CVE was provided in the context.
• Product or platform documentation relevant to the fix: PHP documentation on secure coding practices: https://www.php.net/manual/en/security.input.html