How to remediate – ExtCalendar Detection

1. Introduction

ExtCalendar is a PHP-based web calendar system. It allows users to manage events and schedules through a web interface. This vulnerability means that an attacker could potentially exploit weaknesses in the software, leading to unauthorized access or control of the application. Confidentiality, integrity, and availability may be impacted if exploited.

2. Technical Explanation

ExtCalendar is no longer actively maintained, leaving it vulnerable to known security issues. The standalone version of ExtCalendar has been detected, which differs from instances embedded within other web applications. An attacker could exploit vulnerabilities in the PHP code to gain access to sensitive data or execute arbitrary commands on the server.

• Root cause: Lack of ongoing security updates and maintenance for the ExtCalendar application.
• Exploit mechanism: Attackers can leverage known vulnerabilities within the PHP codebase, potentially through techniques like SQL injection or cross-site scripting (XSS).
• Scope: Standalone installations of ExtCalendar are affected.

3. Detection and Assessment

To confirm a system is vulnerable, you can check for the presence of ExtCalendar files or identify its version through web server responses. Scanning tools may also detect it based on known signatures.

• Quick checks: Check for the existence of ExtCalendar directories and files within your web root directory.
• Scanning: Nessus can identify ExtCalendar installations using signature IDs related to PHP-based calendar systems.
• Logs and evidence: Review web server logs for requests accessing ExtCalendar specific URLs or files.

ls /var/www/html/extcal/ # Example command to list ExtCalendar files in a typical web root directory

4. Solution / Remediation Steps

The recommended solution is to replace ExtCalendar with a supported and actively maintained calendar application due to the lack of security updates for this software.

4.1 Preparation

• Ensure you have a replacement calendar system ready for deployment and that user data can be migrated. A roll back plan involves restoring the original backup.
• A change window may be needed, depending on service impact. Approval from relevant IT stakeholders is recommended.

4.2 Implementation

1. Step 1: Back up the ExtCalendar database and files.
2. Step 2: Remove all ExtCalendar files and directories from the web server.
3. Step 3: Deploy the new calendar application to the server.
4. Step 4: Configure the new calendar system and migrate any existing data.

4.3 Config or Code Example

Before

# ExtCalendar files present in web root directory

After

# No ExtCalendar files found in web root directory. New calendar application deployed.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue. Keeping software up-to-date is crucial, as well as regularly reviewing and patching systems for known vulnerabilities. Least privilege access helps limit the impact if a system is compromised.

• Practice 1: Patch cadence – Regularly update all software to address security vulnerabilities.
• Practice 2: Least privilege – Limit user accounts’ permissions to only what they need.

4.5 Automation (Optional)

# Example Bash script to remove ExtCalendar files (use with caution!)
# rm -rf /var/www/html/extcal/* 

5. Verification / Validation

Confirm the fix by verifying that all ExtCalendar files have been removed and the new calendar application is functioning correctly. Re-run detection methods to ensure no traces of ExtCalendar remain. Perform a smoke test to confirm key functionalities are working as expected.

• Post-fix check: `ls /var/www/html/extcal/` should return “No such file or directory”.
• Re-test: Nessus scans should no longer detect ExtCalendar.
• Smoke test: Verify users can log in to the new calendar system and create events.

ls /var/www/html/extcal/ # Expected output: No such file or directory

6. Preventive Measures and Monitoring

Update security baselines to include a check for unsupported software like ExtCalendar. Implement automated scanning in CI/CD pipelines to identify vulnerable components during deployment. Establish a regular patch review cycle to address known vulnerabilities promptly.

• Baselines: Update your security baseline or policy to prohibit the use of unsupported applications.
• Pipelines: Add static application security testing (SAST) tools to your CI/CD pipeline to detect vulnerable components.
• Asset and patch process: Implement a monthly review cycle for software vulnerabilities.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Data loss during migration – Verify backups and test the migration process thoroughly.
• Risk or side effect 2: Service disruption – Plan for downtime and communicate with users in advance.
• Roll back: Restore the ExtCalendar database and files from the backup created in Step 4.1.

8. References and Resources

• Vendor advisory or bulletin: https://sourceforge.net/projects/extcal/