How to remediate – Web Application Scanner

1. Introduction

The Web Application Scanner vulnerability detects weaknesses in web applications and website files. It helps find potential entry points for attackers targeting online services. Businesses need to address this because successful exploitation can lead to data breaches, service disruption, or website defacement. This affects any organisation running a public-facing website or web application. A typical impact is loss of confidentiality, integrity, and availability of web content and associated data.

2. Technical Explanation

This vulnerability arises from flaws in the code or configuration of web applications. Attackers can exploit these weaknesses to gain unauthorised access or control. Exploitation typically involves sending malicious requests to a vulnerable endpoint. Preconditions include having network connectivity to the target application and identifying exploitable endpoints.

• Root cause: Missing input validation, allowing attackers to inject harmful code or commands into web applications.
• Exploit mechanism: An attacker could submit crafted HTTP requests containing malicious payloads designed to execute arbitrary code on the server. For example, a SQL injection attack targeting a vulnerable login form.
• Scope: Web servers running PHP, ASP.NET, Java, Python and other common web application frameworks are affected. Specific versions depend on the underlying framework and associated libraries.

3. Detection and Assessment

Confirming vulnerability requires checking for known weaknesses in your web applications. Start with a quick review of recent changes and configurations. A thorough assessment involves running a dedicated web application scanner.

• Quick checks: Check the version of your web server software using commands like apachectl -v or httpd -v for Apache, or by reviewing IIS Manager settings for Microsoft IIS.
• Scanning: Nessus vulnerability scanner ID 87069 can identify common web application vulnerabilities. Other scanners such as OpenVAS and Burp Suite also provide similar functionality. These are examples only.
• Logs and evidence: Examine web server access logs for unusual requests or error messages related to input validation failures. Look for patterns indicating attempted exploitation, such as SQL injection attempts or cross-site scripting payloads.

apachectl -v

4. Solution / Remediation Steps

Fixing this issue requires addressing the underlying code and configuration weaknesses in your web applications. Follow these steps to remediate the vulnerability.

4.1 Preparation

• Ensure you have access to the source code or configuration files for the vulnerable applications. A roll back plan involves restoring from the pre-fix backup.
• Changes may require a scheduled maintenance window and approval from relevant stakeholders.

4.2 Implementation

1. Step 1: Implement robust input validation on all user-supplied data to prevent injection attacks.
2. Step 2: Update your web application framework and associated libraries to the latest stable versions, which often include security patches.
3. Step 3: Configure secure headers such as Content Security Policy (CSP) to mitigate cross-site scripting vulnerabilities.
4. Step 4: Review and harden your web server configuration to disable unnecessary features and protect against common attacks.

4.3 Config or Code Example

Before

// Insecure code example (PHP)
$username = $_POST['username'];
$query = "SELECT * FROM users WHERE username = '$username'";

After

// Secure code example (PHP)
$username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $username);
$stmt->execute();

4.4 Security Practices Relevant to This Vulnerability

Several security practices directly address this vulnerability type. Consider implementing least privilege, input validation, and a regular patch cadence.

• Practice 1: Least privilege reduces the impact if an attacker gains access by limiting what they can do.
• Practice 2: Input validation blocks unsafe data from reaching your application code, preventing injection attacks.

4.5 Automation (Optional)

# Example Bash script to check for vulnerable versions of Apache modules
#!/bin/bash
for module in $(apachectl -M | awk '{print $1}'); do
  version=$(apachectl -M | grep "$module" | awk '{print $2}')
  if [[ "$version" == "2.4.50" ]]; then
    echo "Vulnerable Apache module found: $module version $version"
  fi
done

5. Verification / Validation

Confirm the fix by re-running your vulnerability scan and verifying that the issue is no longer detected. Perform a simple service smoke test to ensure functionality remains intact.

• Post-fix check: Run apachectl -M and confirm the web server modules are updated to secure versions.
• Re-test: Re-run the Nessus scan (ID 87069) or other vulnerability scanner to verify that the issue is resolved.
• Smoke test: Test key user actions such as logging in, submitting forms, and browsing web pages to ensure functionality remains unaffected.
• Monitoring: Monitor web server logs for any unusual activity or error messages related to input validation failures. Example query: grep “injection attempt” /var/log/apache2/access.log

apachectl -M

6. Preventive Measures and Monitoring

Update security baselines, add checks in CI pipelines, and establish a sensible patch review cycle to prevent similar issues. For example, use CIS controls or GPO/Intune settings.

• Baselines: Update your security baseline to include requirements for input validation and secure coding practices.
• Asset and patch process: Implement a regular patch review cycle to ensure timely application of security updates.

7. Risks, Side Effects, and Roll Back

Applying patches or configuration changes may introduce compatibility issues or service disruptions. Have a roll back plan in place.

• Risk or side effect 2: Incorrect configuration changes can lead to service outages. Mitigation: Document all changes and have a roll back plan ready.
• Roll back: Restore from the pre-fix backup of your web application files and database. Revert any configuration changes made during the remediation process.

8. References and Resources

• Vendor advisory or bulletin: http://www.nessus.org/u?db90e0fd
• NVD or CVE entry: Not applicable in this context.
• Product or platform documentation relevant to the fix: Refer to your web server and application framework documentation for specific security guidance.