How to remediate – php-Charts url.php Remote PHP Code Execution

1. Introduction

2. Technical Explanation

The vulnerability stems from unsanitized user input passed to the ‘wizard/url.php’ script which is then directly used within a PHP eval() function call. This allows an attacker to inject malicious code that will be executed by the server. An unauthenticated, remote attacker can exploit this flaw.

• Root cause: The application fails to validate user-supplied input before passing it to the eval() function.
• Exploit mechanism: An attacker sends a crafted HTTP request containing malicious PHP code in the relevant parameter of ‘wizard/url.php’. This code is then executed by the server. For example, an attacker could inject code to read sensitive files or establish a reverse shell.
• Scope: Affected systems are those running php-Charts with vulnerable versions installed. Specific version information isn’t available in the provided context.

3. Detection and Assessment

You can check if your system is vulnerable by verifying the presence of the affected script and attempting to identify its behaviour. A thorough scan using a vulnerability scanner will also help.

• Quick checks: Check for the existence of the ‘wizard/url.php’ file within your php-Charts installation directory.
• Scanning: Nessus ID 6e66577d may detect this vulnerability, but results should be verified manually.
• Logs and evidence: Examine web server access logs for requests to ‘wizard/url.php’. Look for unusual characters or patterns in the request parameters that might indicate an attempted exploit.

ls -l /path/to/php-charts/wizard/url.php

4. Solution / Remediation Steps

Currently, a specific solution isn’t known for this vulnerability. The following steps outline general best practices to mitigate the risk while awaiting an official patch.

4.1 Preparation

• There are no known dependencies or pre-requisites for mitigation, but it is advisable to perform these steps during a scheduled maintenance window. A roll back plan involves restoring from your backup.
• Changes should be approved by a senior IT administrator.

4.2 Implementation

1. Step 1: Disable access to the ‘wizard/url.php’ script through web server configuration (e.g., .htaccess, Nginx config). This is a temporary measure until a patch is available.
2. Step 2: Monitor web server logs for any attempts to access the disabled script.
3. Step 3: Regularly check for updates and patches from the php-Charts vendor.

4.3 Config or Code Example

Before

# No specific configuration example available, as the vulnerability is within the application code itself. Access to wizard/url.php is allowed by default.

After

# Example .htaccess file entry to deny access:
<Files "wizard/url.php">
  Order Deny,Allow
  Deny from all
</Files>

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 2: Least Privilege – Run web applications with the minimum necessary privileges to limit the impact of a successful exploit.

4.5 Automation (Optional)

No automation script is available at this time.

5. Verification / Validation

• Post-fix check: Attempt to access ‘wizard/url.php’ through your web browser. The expected output is a 403 Forbidden or similar error message.
• Re-test: Run the earlier detection method (checking for the existence of ‘wizard/url.php’) and confirm that it still exists but is inaccessible.
• Smoke test: Verify other core features of php-Charts are functioning as expected, such as chart creation and data display.

curl -I http://your-phpcharts-server/wizard/url.php

6. Preventive Measures and Monitoring

Update security baselines to include input validation requirements for web applications. Implement regular vulnerability scanning in CI/CD pipelines.

• Baselines: Update your web application security baseline to require strict input validation and sanitisation of all user-supplied data.
• Pipelines: Integrate a Static Application Security Testing (SAST) tool into your CI/CD pipeline to identify potential vulnerabilities like this one during development.
• Asset and patch process: Implement a regular patch review cycle for all web applications, including php-Charts.

7. Risks, Side Effects, and Roll Back

Disabling access to ‘wizard/url.php’ may impact functionality if it is used by legitimate features of the application. The roll back steps involve re-enabling access through your web server configuration.

• Risk or side effect 1: Disabling ‘wizard/url.php’ could break existing charts or reports that rely on this script.
• Risk or side effect 2: Users may encounter errors if they attempt to use features dependent on the disabled script.
• Roll back: Remove the configuration changes made in Step 1 of the Implementation section to re-enable access to ‘wizard/url.php’.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory is available in the provided context.
• NVD or CVE entry: http://www.nessus.org/u?6e66577d
• Product or platform documentation relevant to the fix: No specific product documentation is available in the provided context.