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Defending Against Pass-the-Hash (PtH) Attacks: Practical Strategies

Preparation: Maintaining Control of Hashes

1. Use Host Firewalls to Block Client-to-Client Connections

  • Implement host-based firewalls on client machines to restrict SMB connections. Allow inbound SMB traffic only from designated administrative systems. This prevents attackers from moving laterally across the network using stolen hashes.


2. Manage Local Administrator Passwords with Microsoft Local Administrator Password Solution (LAPS)

  • Deploy LAPS to enforce unique and complex passwords for local Administrator accounts on each workstation. This minimizes the risk of one compromised Administrator password being used to access multiple systems. More information and download links for LAPS can be found here.


3. Deploy Microsoft Credential Guard

  • Leverage Microsoft Credential Guard to isolate critical credential information using virtualization-based security. This makes it more difficult for attackers to access password hashes. Credential Guard helps protect against credential theft by securing LSASS and other sensitive processes. Learn more about Credential Guard here.


Identification: Detecting Unusual Activity

1. Monitor for Unusual Administrative Activities

  • Track changes in system configurations and look for signs of unexpected administrative actions. This includes monitoring logs for unusual patterns that could indicate an attempt to use stolen credentials.


2. Detect Unusual Machine-to-Machine Connections

  • Watch for unusual SMB connections, such as clients attempting to mount shares on other clients or servers connecting to servers in atypical ways. Tools like net session can list active SMB sessions on the destination system, helping to identify unauthorized connections.


Containment, Eradication, and Recovery

1. Change Passwords Immediately

  • If you suspect that password hashes have been compromised, change the passwords on all affected systems promptly. This limits the window of opportunity for attackers to use stolen hashes for further access.


2. Use Comprehensive Endpoint Security Suites

  • Ensure your endpoints are protected with robust security suites that include antivirus, antispyware, personal firewall, and host-based IPS technologies. Regularly update and patch these tools to address new vulnerabilities and threats.


3. Implement Strong Password Policies

  • Enforce strong password policies to reduce the likelihood of hash theft. This includes using complex passwords, enabling multi-factor authentication (MFA), and educating users about the importance of secure password practices.


Conclusion

Pass-the-Hash attacks continue to be a significant security concern. By implementing these strategies, organizations can better prepare for, detect, and mitigate PtH attacks. Key defenses include using host firewalls, managing local Administrator passwords with LAPS, and deploying Microsoft Credential Guard. Additionally, monitoring for unusual activities and quickly responding to suspected compromises are critical for maintaining a secure environment.


Akash Patel

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