Dynamic-link libraries (DLLs) that are specified in the AppCertDLLs value in the Registry key
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager are loaded into every process that calls the ubiquitously used application programming interface (API) functions CreateProcess, CreateProcessAsUser, CreateProcessWithLoginW, CreateProcessWithTokenW, or WinExec. 
Similar to Process Injection, this value can be abused to obtain persistence and privilege escalation by causing a malicious DLL to be loaded and run in the context of separate processes on the computer.
Identify and block potentially malicious software that may be executed through AppCert DLLs by using whitelisting  tools, like AppLocker,   that are capable of auditing and/or blocking unknown DLLs.
Monitor DLL loads by processes, specifically looking for DLLs that are not recognized or not normally loaded into a process. Monitor the AppCertDLLs Registry value for modifications that do not correlate with known software, patch cycles, etc. Monitor and analyze application programming interface (API) calls that are indicative of Registry edits such as RegCreateKeyEx and RegSetValueEx. 
Look for abnormal process behavior that may be due to a process loading a malicious DLL. Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities, such as making network connections for Command and Control, learning details about the environment through Discovery, and conducting Lateral Movement.
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- NSA Information Assurance Directorate. (2014, August). Application Whitelisting Using Microsoft AppLocker. Retrieved March 31, 2016.
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- Microsoft. (2007, October 24). Windows Sysinternals - AppCertDlls. Retrieved December 18, 2017.