DLL Search Order Hijacking

Disallow loading of remote DLLs. (Citation: Microsoft DLL Preloading) This is included by default in Windows Server 2012+ and is available by patch for XP+ and Server 2003+. (Citation: Microsoft DLL Search) Path Algorithm Enable Safe DLL Search Mode to force search for system DLLs in directories with greater restrictions (e.g. %SYSTEMROOT%)to be used before local directory DLLs (e.g. a user's home directory). The Safe DLL Search Mode can be enabled via Group Policy at Computer Configuration > [Policies] > Administrative Templates > MSS (Legacy): MSS: (SafeDllSearchMode) Enable Safe DLL search mode. The associated Windows Registry key for this is located at HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\SafeDLLSearchMode (Citation: Microsoft DLL Search) Use auditing tools capable of detecting DLL search order hijacking opportunities on systems within an enterprise and correct them. Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for DLL hijacking weaknesses. (Citation: Powersploit) Identify and block potentially malicious software that may be executed through search order hijacking by using whitelisting (Citation: Beechey 2010) tools like AppLocker (Citation: Windows Commands JPCERT) (Citation: NSA MS AppLocker) that are capable of auditing and/or blocking unknown DLLs.

Auditing is the process of recording activity and systematically reviewing and analyzing the activity and system configurations. The primary purpose of auditing is to detect anomalies and identify potential threats or weaknesses in the environment. Proper auditing configurations can also help to meet compliance requirements. The process of auditing encompasses regular analysis of user behaviors and system logs in support of proactive security measures. Auditing is applicable to all systems used within an organization, from the front door of a building to accessing a file on a fileserver. It is considered more critical for regulated industries such as, healthcare, finance and government where compliance requirements demand stringent tracking of user and system activates.This mitigation can be implemented through the following measures: System Audit: - Use Case: Regularly assess system configurations to ensure compliance with organizational security policies. - Implementation: Use tools to scan for deviations from established benchmarks. Permission Audits: - Use Case: Review file and folder permissions to minimize the risk of unauthorized access or privilege escalation. - Implementation: Run access reviews to identify users or groups with excessive permissions. Software Audits: - Use Case: Identify outdated, unsupported, or insecure software that could serve as an attack vector. - Implementation: Use inventory and vulnerability scanning tools to detect outdated versions and recommend secure alternatives. Configuration Audits: - Use Case: Evaluate system and network configurations to ensure secure settings (e.g., disabled SMBv1, enabled MFA). - Implementation: Implement automated configuration scanning tools like SCAP (Security Content Automation Protocol) to identify non-compliant systems. Network Audits: - Use Case: Examine network traffic, firewall rules, and endpoint communications to identify unauthorized or insecure connections. - Implementation: Utilize tools such as Wireshark, or Zeek to monitor and log suspicious network behavior.

Prevent the execution of unauthorized or malicious code on systems by implementing application control, script blocking, and other execution prevention mechanisms. This ensures that only trusted and authorized code is executed, reducing the risk of malware and unauthorized actions. This mitigation can be implemented through the following measures: Application Control: - Use Case: Use tools like AppLocker or Windows Defender Application Control (WDAC) to create whitelists of authorized applications and block unauthorized ones. On Linux, use tools like SELinux or AppArmor to define mandatory access control policies for application execution. - Implementation: Allow only digitally signed or pre-approved applications to execute on servers and endpoints. (e.g., `New-AppLockerPolicy -PolicyType Enforced -FilePath "C:\Policies\AppLocker.xml"`) Script Blocking: - Use Case: Use script control mechanisms to block unauthorized execution of scripts, such as PowerShell or JavaScript. Web Browsers: Use browser extensions or settings to block JavaScript execution from untrusted sources. - Implementation: Configure PowerShell to enforce Constrained Language Mode for non-administrator users. (e.g., `Set-ExecutionPolicy AllSigned`) Executable Blocking: - Use Case: Prevent execution of binaries from suspicious locations, such as `%TEMP%` or `%APPDATA%` directories. - Implementation: Block execution of `.exe`, `.bat`, or `.ps1` files from user-writable directories. Dynamic Analysis Prevention: - Use Case: Use behavior-based execution prevention tools to identify and block malicious activity in real time. - Implemenation: Employ EDR solutions that analyze runtime behavior and block suspicious code execution.

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.