Threat Overview

The Security Operations Center (SOC) has identified a new and sophisticated threat report published by AlienVault on May 15, 2025. The report, titled Excel Obfuscation: Regex Gone Rogue, details an advanced attack technique that leverages recently introduced regex functions in Excel for code obfuscation.

Threat Actor Group

The specific actor group responsible for this technique has not been identified in the report. However, the sophistication of the method suggests a well-resourced and skilled adversary.

Detailed Threat Description

This new attack technique utilizes Excel’s REGEXEXTRACT function to hide PowerShell commands within large text blocks. By doing so, malicious actors can significantly reduce the detection rates by antivirus software. The proof-of-concept demonstrates that this method drops VirusTotal detections from 22 to just 2, making it much harder for traditional security measures to identify and mitigate the threat.

The technique outperforms traditional obfuscation methods by evading heuristic analysis tools like OLEVBA. This makes it a potent tool in the arsenal of cybercriminals seeking to bypass conventional security defenses.

Current Limitations

While this method is highly effective, it is currently limited by Microsoft’s default macro security settings and the limited availability of the regex functions. These limitations reduce the immediate threat but do not eliminate it entirely. As these functions become more widely accessible, the technique could be combined with other sophisticated attack methods to create even more formidable threats.

Recommendations for Mitigation

1. Enhance Macro Security Settings: Ensure that all systems have Microsoft’s default macro security settings enabled and consider implementing stricter policies to block macros from running in Excel files received from untrusted sources.

2. Regular Software Updates: Keep all software, including Excel and antivirus programs, up-to-date with the latest patches and updates. This helps in mitigating known vulnerabilities that could be exploited by such techniques.

3. Advanced Threat Detection Tools: Deploy advanced threat detection tools that go beyond traditional antivirus solutions. These tools should include behavior-based analysis and machine learning capabilities to identify and mitigate sophisticated obfuscation techniques.

4. Employee Training: Conduct regular training sessions for employees on recognizing phishing attempts and suspicious email attachments. Educating the workforce about the dangers of macros in Excel files can significantly reduce the risk of successful attacks.

5. Network Monitoring: Implement robust network monitoring solutions to detect unusual activities that may indicate a breach. This includes monitoring for unauthorized access, data exfiltration, and other malicious behaviors.

6. Incident Response Plan: Develop and regularly update an incident response plan to quickly identify, contain, and mitigate any security breaches. Ensure that all employees are familiar with the plan and their roles in executing it.

7. Regular Security Audits: Conduct regular security audits to identify vulnerabilities in the system. This includes penetration testing and vulnerability assessments to ensure that all potential entry points are secured.

8. Use of Sandboxing: Implement sandboxing techniques to isolate and analyze suspicious files in a controlled environment before they can cause any damage to the main network.

9. Multi-Factor Authentication (MFA): Enforce MFA for accessing critical systems and data. This adds an extra layer of security, making it harder for attackers to gain unauthorized access even if they manage to bypass initial defenses.

10. Collaboration with Security Communities: Stay informed about the latest threats and vulnerabilities by collaborating with security communities and sharing threat intelligence. This helps in staying ahead of emerging threats and adapting defense strategies accordingly.

Conclusion

The Excel Obfuscation: Regex Gone Rogue technique represents a significant advancement in cyber threats, leveraging modern features to evade detection. While current limitations reduce its immediate impact, the potential for future exploitation is high. By implementing robust security measures and staying vigilant, organizations can mitigate this threat and protect their systems from sophisticated attacks.

For additional information, please refer to the following external references:

1. Deep Instinct Blog: https://www.deepinstinct.com/blog/excellent-obfuscation-regex-gone-rogue
2. AlienVault OTX Pulse: https://otx.alienvault.com/pulse/6825f54fef573f818bd2d43c

Please check the following page for additional information:

https://www.deepinstinct.com/blog/excellent-obfuscation-regex-gone-rogue