Potential Evasion via Windows Filtering Platform Blocking Security Software

The Windows Filtering Platform (WFP) provides APIs and system services for network filtering and packet processing. Attackers can abuse WFP by creating malicious rules to block endpoint security processes, hindering their ability to send telemetry. This can be achieved by tools like Shutter, EDRSilencer, and Nighthawk. This detection rule identifies patterns of blocked network events linked to security software processes, signaling potential evasion tactics. The rule specifically looks for blocked network events linked to processes associated with known security software, aiming to detect and alert on attempts to disable or modify security tools. This behavior is especially concerning as it allows attackers to operate with reduced visibility.

Attack Chain

1. Attacker gains initial access to the target system (e.g., via compromised credentials or exploiting a vulnerability).
2. The attacker escalates privileges to gain administrative rights, necessary to interact with the Windows Filtering Platform.
3. The attacker uses a tool or script (e.g., leveraging the netsh command or custom WFP API calls) to create a new WFP filter.
4. The WFP filter is configured to block network traffic originating from specific processes associated with endpoint security software (e.g., elastic-agent.exe, sysmon.exe).
5. The system begins blocking network communication from the targeted security software.
6. The attacker executes malicious commands or malware on the system, knowing that security telemetry will be suppressed.
7. The attacker moves laterally within the network, repeating the WFP filter deployment on other systems to further impair defenses.
8. The attacker achieves their final objective, such as data exfiltration or ransomware deployment, with reduced risk of detection.

Impact

A successful attack using WFP to impair defenses can lead to a significant reduction in the effectiveness of endpoint security solutions. This can result in delayed detection of malicious activities, increased dwell time for attackers, and ultimately, a higher likelihood of successful data breaches or ransomware attacks. With endpoint telemetry blocked, organizations may remain unaware of the ongoing compromise until significant damage has occurred. The number of affected systems can vary depending on the attacker’s scope and objectives.

Recommendation

• Enable and review Windows Audit Filtering Platform Connection and Packet Drop events to populate the logs required for the provided EQL rule (logs-system.security*, logs-windows.forwarded*, winlogbeat-*).
• Deploy the provided EQL rule to your SIEM to detect suspicious WFP modifications and tune for your environment.
• Investigate any alerts generated by the EQL rule, focusing on identifying the specific processes being blocked and the source of the WFP rule modifications.
• Regularly review and audit WFP rules to identify any unauthorized or suspicious entries.
• Implement strict access controls and monitoring for systems authorized to modify WFP rules.