Restrict Library Loading

Restricting library loading involves implementing security controls to ensure that only trusted and verified libraries (DLLs, shared objects, etc.) are loaded into processes. Adversaries often abuse Dynamic-Link Library (DLL) Injection, DLL Search Order Hijacking, or LD_PRELOAD mechanisms to execute malicious code by forcing the operating system to load untrusted libraries. This mitigation can be implemented through the following measures:

Enforce Safe Library Loading Practices:

• Enable SafeDLLSearchMode on Windows.
• Restrict LD_PRELOAD and LD_LIBRARY_PATH usage on Linux systems.

Code Signing Enforcement:

• Require digital signatures for all libraries loaded into processes.
• Use tools like Signtool, and WDAC to enforce signed DLL execution.

Environment Hardening:

• Secure library paths and directories to prevent adversaries from placing rogue libraries.
• Monitor user-writable directories and system configurations for unauthorized changes.

Audit and Monitor Library Loading:

• Enable Sysmon on Windows to monitor for suspicious library loads.
• Use auditd on Linux to monitor shared library paths and configuration file changes.

Use Application Control Solutions:

• Implement AppLocker, WDAC, or SELinux to allow only trusted libraries.

Tools for Implementation

Windows-Specific Tools:

• AppLocker: Application whitelisting for DLLs.
• Windows Defender Application Control (WDAC): Restrict unauthorized library execution.
• Signtool: Verify and enforce code signing.
• Sysmon: Monitor DLL load events (Event ID 7).

Linux-Specific Tools:

• auditd: Monitor changes to library paths and critical files.
• SELinux/AppArmor: Define policies to restrict library loading.
• ldconfig and chattr: Secure LD configuration files and prevent unauthorized modifications.

Cross-Platform Solutions:

• Wazuh or OSSEC: File integrity monitoring for library changes.
• Tripwire: Detect and alert on unauthorized library modifications.