How to remediate – YARA Scan Cleanup (Linux)

1. Introduction

2. Technical Explanation

The Yara Scan Cleanup removes files installed during a previous scan operation. The temporary installation directory and associated Yara rules are deleted from the system. This prevents re-running of those specific scans, but does not address any vulnerabilities in the original scanned applications. An attacker with local access could potentially restore these files if they have sufficient permissions or backups exist.

• Exploit mechanism: An attacker with local access restores the deleted Yara rules and installation, then runs them to identify sensitive information or trigger false positives.
• Scope: Linux systems where Yara scans have been performed.

3. Detection and Assessment

Confirming whether a system requires cleanup involves checking for the presence of files associated with the Yara scan. A quick check can verify if the installation directory exists, while a thorough method lists all related files.

• Quick checks: Check for the existence of the temporary installation directory using ls /tmp/yara_scan or similar path depending on configuration.
• Scanning: No common scanner signatures are directly applicable to this cleanup process itself.
• Logs and evidence: Review system logs for file creation events related to Yara installations, typically in /var/log/syslog or similar.

ls /tmp/yara_scan

4. Solution / Remediation Steps

These steps remove the residual files from a previous Yara scan operation on Linux systems. They are designed to be safe and easily reversible if needed.

4.1 Preparation

• Dependencies: None. Change window needs are minimal; standard IT maintenance windows apply. Approval may not be required unless part of a wider security process.

4.2 Implementation

1. Step 1: Remove the temporary Yara installation directory using rm -rf /tmp/yara_scan (adjust path if necessary).
2. Step 2: Verify that all related files have been removed by listing the contents of the original installation directory.

4.3 Config or Code Example

Before

ls /tmp/yara_scan

After

ls /tmp/yara_scan  (should return no output)

4.4 Security Practices Relevant to This Vulnerability

Practices that directly address this vulnerability type include secure defaults and a patch cadence for security tools. Least privilege is also relevant, as it limits the impact if an attacker gains access.

• Practice 2: Patch Cadence – Regularly update security scanning tools like Yara to benefit from bug fixes and improved cleanup routines.

4.5 Automation (Optional)

A simple Bash script can automate the cleanup process across multiple systems. Use caution when running scripts with root privileges.

#!/bin/bash
# Script to remove Yara scan directories
for host in $(cat /tmp/host_list); do
  ssh $host "rm -rf /tmp/yara_scan"
done

5. Verification / Validation

Confirming the fix involves verifying that the temporary files have been removed and re-running the detection check to ensure no traces remain. A simple service smoke test is not applicable in this case, as it does not directly impact system functionality.

• Post-fix check: Run ls /tmp/yara_scan; expected output should be empty or an error message indicating the directory does not exist.
• Re-test: Re-run the earlier detection check (ls /tmp/yara_scan) to confirm no files are present.
• Smoke test: Not applicable.
• Monitoring: Monitor system logs for unexpected file creation events in /tmp or similar directories, as an example.

ls /tmp/yara_scan (should return no output)

6. Preventive Measures and Monitoring

• Baselines: Update a security baseline or policy to enforce automatic removal of temporary files created by security scanning tools.
• Pipelines: Include configuration validation checks in CI/CD pipelines to ensure Yara scans are set up with automatic cleanup enabled.
• Asset and patch process: Implement a regular review cycle for security tool configurations, including Yara scan settings.

7. Risks, Side Effects, and Roll Back

The primary risk is accidentally deleting important files if the installation path is incorrect. The side effect could be loss of scan history or results if they were stored in the temporary directory. Roll back involves restoring any deleted files from a backup.

• Risk or side effect 2: Loss of scan history if stored in the temporary directory; mitigate by storing scan results elsewhere.
• Roll back: Restore any deleted files from a backup, if available.

8. References and Resources

• Vendor advisory or bulletin: http://virustotal.github.io/yara/
• NVD or CVE entry: Not applicable, as this is a cleanup process rather than a vulnerability itself.
• Product or platform documentation relevant to the fix: http://virustotal.github.io/yara/ (YARA documentation on file management).