Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by accessibility features. Windows contains accessibility features that may be launched with a key combination before a user has logged in (ex: when the user is on the Windows logon screen). An adversary can modify the way these programs are launched to get a command prompt or backdoor without logging in to the system.
Two common accessibility programs are <code>C:\Windows\System32\sethc.exe</code>, launched when the shift key is pressed five times and <code>C:\Windows\System32\utilman.exe</code>, launched when the Windows + U key combination is pressed. The sethc.exe program is often referred to as "sticky keys", and has been used by adversaries for unauthenticated access through a remote desktop login screen. (Citation: FireEye Hikit Rootkit)
Depending on the version of Windows, an adversary may take advantage of these features in different ways. Common methods used by adversaries include replacing accessibility feature binaries or pointers/references to these binaries in the Registry. In newer versions of Windows, the replaced binary needs to be digitally signed for x64 systems, the binary must reside in <code>%systemdir%\</code>, and it must be protected by Windows File or Resource Protection (WFP/WRP). (Citation: DEFCON2016 Sticky Keys) The Image File Execution Options Injection debugger method was likely discovered as a potential workaround because it does not require the corresponding accessibility feature binary to be replaced.
For simple binary replacement on Windows XP and later as well as and Windows Server 2003/R2 and later, for example, the program (e.g., <code>C:\Windows\System32\utilman.exe</code>) may be replaced with "cmd.exe" (or another program that provides backdoor access). Subsequently, pressing the appropriate key combination at the login screen while sitting at the keyboard or when connected over Remote Desktop Protocol will cause the replaced file to be executed with SYSTEM privileges. (Citation: Tilbury 2014)
Other accessibility features exist that may also be leveraged in a similar fashion: (Citation: DEFCON2016 Sticky Keys)(Citation: Narrator Accessibility Abuse)
Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
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CM-10 | Software Usage Restrictions | Protects | T1546.008 | Accessibility Features | |
CM-6 | Configuration Settings | Protects | T1546.008 | Accessibility Features | |
CM-7 | Least Functionality | Protects | T1546.008 | Accessibility Features | |
SI-10 | Information Input Validation | Protects | T1546.008 | Accessibility Features | |
SI-4 | System Monitoring | Protects | T1546.008 | Accessibility Features | |
SI-7 | Software, Firmware, and Information Integrity | Protects | T1546.008 | Accessibility Features |
Capability ID | Capability Description | Mapping Type | ATT&CK ID | ATT&CK Name | Notes |
---|---|---|---|---|---|
alerts_for_windows_machines | Alerts for Windows Machines | technique_scores | T1546.008 | Accessibility Features |
Comments
This control may detect when the binary for the sticky keys utility has been replaced, possibly to gain persistence or execution. The following alerts may be generated: "Sticky keys attack detected".
References
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azure_sentinel | Azure Sentinel | technique_scores | T1546.008 | Accessibility Features |
Comments
The Azure Sentinel Analytics "Powershell Empire cmdlets seen in command line" query can detect the use of Empire, which can leverage WMI debugging to remotely replace binaries like seth.exe, utilman.exe, and magnify.exe with cmd.exe, but does not address other procedures.
References
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file_integrity_monitoring | File Integrity Monitoring | technique_scores | T1546.008 | Accessibility Features |
Comments
This control may detect changes to the Windows registry or files that indicate event triggered execution. The specificity of registry keys and files used in creation or modification of these scheduled tasks may reduce the false positive rate. This control at worst scans for changes on an hourly basis.
References
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