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 AppCertDLLs Registry key under 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. [1]
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.
| ID | Name | Description |
|---|---|---|
| S0196 | PUNCHBUGGY |
PUNCHBUGGY can establish using a AppCertDLLs Registry key.[2] |
| ID | Mitigation | Description |
|---|---|---|
| M1038 | Execution Prevention |
Adversaries install new AppCertDLL binaries to execute this technique. Identify and block potentially malicious software executed through AppCertDLLs functionality by using application control [3] tools, like Windows Defender Application Control[4], AppLocker, [5] [6] or Software Restriction Policies [7] where appropriate. [8] |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0362 | Detection Strategy for AppCert DLLs Persistence via Registry Injection | AN1029 |
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. |