T1546.009 AppCert DLLs — Attack Pattern

Description

Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by AppCert DLLs loaded into processes. Dynamic-link libraries (DLLs) that are specified in the <code>AppCertDLLs</code> Registry key under <code>HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\</code> are loaded into every process that calls the ubiquitously used application programming interface (API) functions <code>CreateProcess</code>, <code>CreateProcessAsUser</code>, <code>CreateProcessWithLoginW</code>, <code>CreateProcessWithTokenW</code>, or <code>WinExec</code>. (Citation: Elastic Process Injection July 2017) Similar to Process Injection, this value can be abused to obtain elevated privileges by causing a malicious DLL to be loaded and run in the context of separate processes on the computer. Malicious AppCert DLLs may also provide persistence by continuously being triggered by API activity.

MITRE ATT&CK Detection Strategies
1

DET0362 Detection Strategy for AppCert DLLs Persistence via Registry Injection

AN1029 Windows

Detection of AppCert DLL abuse involves correlating registry modifications to the AppCertDLLs key with subsequent unexpected DLL load behavior during process creation events. Specifically, defenders can observe abnormal DLLs being loaded into standard Windows processes after changes to the 'AppCertDLLs' registry value. Monitoring CreateProcess-family API executions with injected DLLs and linking those DLLs back to recent registry edits is key to identifying misuse. This is often accompanied by elevated privileges and potential lateral movement or discovery behavior.

WinEventLog:Security WinEventLog:Sysmon WinEventLog:Sysmon

MITRE ATT&CK Mitigations
1

M1038

Execution Prevention

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.

AppCert DLLs

Description

MITRE ATT&CK Detection Strategies 1

MITRE ATT&CK Mitigations 1

Details

MITRE ATT&CK Detection Strategies
1

MITRE ATT&CK Mitigations
1