Query: EDR alert: possible Hidden Window (T1564.003)
Matching passage: T1564.003 Hidden Window. Tactics: stealth. Description: Adversaries may use hidden windows to conceal malicious activity from the plain sight of users. In some cases, windows that would typically be displayed when an application carries out an operation can be hidden. This may be utilized by system administrators to avoid disrupting user work environments when carrying out administrative tasks. Adversaries may abuse these functionalities to hide otherwise visible windows from users so as not to alert the user to adversary activity on the system.(Citation: Antiquated Mac Malware) On macOS, the configurations for how applications run are listed in property list (plist) files. One of the tags in these files can be <code>apple.awt.UIElement</code>, which allows for Java applications to prevent the application's icon from appearing in the Dock. A common use for this is when applications run in the system tray, but don't also want to show up in the Dock. Similarly, on Windows there are a variety of features in scripting languages, such as [PowerShell](https://attack.mitre.org/techniques/T1059/001), Jscript, and [Visual Basic](https://attack.mitre.org/techniques/T1059/005) to make windows hidden. One example of this is <code>powershell.exe -WindowStyle Hidden</code>.(Citation: PowerShell About 2019) The Windows Registry can also be edited to hide application windows from the current user. For example, by setting the `WindowPosition` subkey in the `HKEY_CURRENT_USER\Console\%SystemRoot%_System32_WindowsPowerShell_v1.0_PowerShell.exe` Registry key to a maximum value, PowerShell windows will open off screen and be hidden.(Citation: Cantoris Computing) In addition, Windows supports the `CreateDesktop()` API that can create a hidden desktop window with its own corresponding <code>explorer.exe</code> process.(Citation: Hidden VNC)(Citation: Anatomy of an hVNC Attack) All applications running on the hidden desktop window, such as a hidden VNC (hVNC) session,(Citation: Hidden VNC) will be invisible to other desktops windows. Adversarie
Near-miss passage: T1564.011 Ignore Process Interrupts. Tactics: stealth. Description: Adversaries may evade defensive mechanisms by executing commands that hide from process interrupt signals. Many operating systems use signals to deliver messages to control process behavior. Command interpreters often include specific commands/flags that ignore errors and other hangups, such as when the user of the active session logs off.(Citation: Linux Signal Man) These interrupt signals may also be used by defensive tools and/or analysts to pause or terminate specified running processes. Adversaries may invoke processes using `nohup`, [PowerShell](https://attack.mitre.org/techniques/T1059/001) `-ErrorAction SilentlyContinue`, or similar commands that may be immune to hangups.(Citation: nohup Linux Man)(Citation: Microsoft PowerShell SilentlyContinue) This may enable malicious commands and malware to continue execution through system events that would otherwise terminate its execution, such as users logging off or the termination of its C2 network connection. Hiding from process interrupt signals may allow malware to continue execution, but unlike [Trap](https://attack.mitre.org/techniques/T1546/005) this does not establish [Persistence](https://attack.mitre.org/tactics/TA0003) since the process will not be re-invoked once actually terminated.