How to remediate – Web Server Malicious JavaScript Link Detection

1. Introduction

Web Server Malicious JavaScript Link Detection indicates your web server is linking to harmful JavaScript code on another website. This usually means an attacker has gained control of your server and could infect visitors with malware. Confidentiality, integrity, and availability may all be affected if the server is fully compromised. Keep this section under 120 words.

2. Technical Explanation

This vulnerability occurs when an attacker injects malicious JavaScript links into your web server’s pages. This typically happens through a weakness in how the server handles user input or dynamic content generation. An attacker could then serve malware to anyone visiting those affected pages.

• Root cause: The root cause is often a SQL injection vulnerability within dynamic pages, allowing an attacker to modify the content served by the webserver.
• Exploit mechanism: An attacker exploits this flaw by injecting malicious JavaScript code into database queries which are then executed and displayed on webpages. For example, they might inject `` into a comment field that isn’t properly sanitised.
• Scope: Web servers running vulnerable applications or content management systems (CMS) are affected. Specific versions depend on the software in use and whether security patches have been applied.

3. Detection and Assessment

You can confirm this vulnerability by checking your web server’s configuration and scanning for malicious code. A quick check is to review recently modified files. A thorough method involves a full website scan.

• Quick checks: Check the modification dates of key webpage files using `ls -l` on Linux or reviewing file properties in Windows Explorer. Look for unexpected changes.
• Scanning: Nessus vulnerability scanner may identify this issue with ID 1698452 (example only). Other web application scanners can also be used.
• Logs and evidence: Examine your web server access logs for unusual requests or files being served from unfamiliar domains. Look for JavaScript file extensions in unexpected locations.

ls -l /var/www/html/*

4. Solution / Remediation Steps

Fixing this issue requires restoring your server and patching vulnerabilities. Follow these steps carefully to ensure a secure recovery.

4.1 Preparation

• Ensure you have access to original website files for restoration. A roll back plan is to restore from the pre-change backup.
• A change window may be needed depending on service impact. Approval from a senior IT administrator might be required.

4.2 Implementation

1. Step 1: Restore your web server to its last known good state using your backup or snapshot.
2. Step 2: Audit all dynamic pages for SQL injection vulnerabilities. Use a code review tool or manual inspection.
3. Step 3: Apply the latest security patches for your web server software and any associated applications (e.g., CMS).

4.3 Config or Code Example

Before

$query = "SELECT * FROM comments WHERE post_id = " . $_GET['post_id']; // Vulnerable code

After

$post_id = (int)$_GET['post_id']; $query = "SELECT * FROM comments WHERE post_id = ?"; $stmt = $pdo->prepare($query); $stmt->execute([$post_id]); // Secure code using prepared statements

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege limits the damage from a compromise. Input validation blocks unsafe data. Patch cadence ensures timely updates.

• Practice 1: Implement least privilege for all web server accounts and processes to reduce the impact if an attacker gains access.
• Practice 2: Use input validation on all user-supplied data to prevent malicious code from being injected into database queries or displayed on webpages.

4.5 Automation (Optional)

# Example Bash script to check for modified files
find /var/www/html -type f -mtime -1 | grep '.php$' # Lists PHP files modified in the last day

5. Verification / Validation

Confirm the fix by checking your server’s configuration and re-scanning for malicious code. A simple service smoke test is to browse key webpages.

• Post-fix check: Verify that all dynamic pages are functioning correctly and no longer contain suspicious JavaScript links.
• Re-test: Re-run the Nessus scan (ID 1698452) or other web application scanner to confirm the vulnerability is resolved.
• Smoke test: Test key user actions, such as submitting a form or viewing comments, to ensure they still work as expected.
• Monitoring: Monitor your web server access logs for any unusual requests or files being served from unfamiliar domains (example only).

ls -l /var/www/html/*

6. Preventive Measures and Monitoring

• Baselines: Update your web server security baseline to require strict input validation and sanitisation of all user-supplied data.
• Asset and patch process: Review and apply security patches for your web server software and associated applications at least monthly, or more frequently if critical vulnerabilities are identified.

7. Risks, Side Effects, and Roll Back

Restoring from a backup may result in data loss. Applying patches could cause temporary service disruptions. A roll back plan is to restore the pre-change backup.

• Risk or side effect 1: Restoring from a backup might overwrite recent changes made to your website, resulting in data loss.
• Risk or side effect 2: Applying security patches could cause temporary service disruptions or compatibility issues with other applications.
• Roll back: Restore the web server from the pre-change backup if any issues occur during the remediation process.

8. References and Resources

• Vendor advisory or bulletin: Check your web server software vendor’s website for specific security advisories related to JavaScript injection vulnerabilities.
• NVD or CVE entry: http://www.nessus.org/u?d8fa1760
• Product or platform documentation relevant to the fix: Refer to your web server software’s documentation for instructions on applying security patches and configuring input validation.