Detect Extra Window Memory Injection in Microsoft Sentinel
Adversaries may inject malicious code into process via Extra Window Memory (EWM) in order to evade process-based defenses as well as possibly elevate privileges. EWM injection is a method of executing arbitrary code in the address space of a separate live process. Before creating a window, graphical Windows-based processes must prescribe to or register a windows class, which stipulate appearance and behavior via windows procedures. Registration of new windows classes can include a request for up to 40 bytes of EWM. Although small, the EWM is large enough to store a 32-bit pointer and is often used to point to a windows procedure. Malware may utilize this memory location in part of an attack chain that includes writing code to shared sections of the process's memory, placing a pointer to the code in EWM, then invoking execution by returning execution control to the address in the process's EWM.
MITRE ATT&CK
- Technique
- T1055 Process Injection
- Sub-technique
- T1055.011 Extra Window Memory Injection
- Canonical reference
- https://attack.mitre.org/techniques/T1055/011/
KQL Detection Query
// Detect EWM injection via suspicious API calls targeting Shell_TrayWnd
// EWM injection targets Explorer's Shell_TrayWnd window class
DeviceEvents
| where Timestamp > ago(24h)
| where ActionType in ("SetWindowLongApiCall", "SendMessageApiCall", "CreateRemoteThreadApiCall")
| where FileName =~ "explorer.exe"
| where InitiatingProcessFileName !in~ ("explorer.exe", "csrss.exe", "dwm.exe", "winlogon.exe", "ShellExperienceHost.exe", "SearchUI.exe")
| project Timestamp, DeviceName, AccountName, ActionType, InitiatingProcessFileName, InitiatingProcessCommandLine, FileName
| sort by Timestamp desc
// Fallback: detect via ProcessAccess to explorer.exe with write rights
| union (
DeviceEvents
| where Timestamp > ago(24h)
| where ActionType == "ProcessAccessedApiCall"
| where FileName =~ "explorer.exe"
| where InitiatingProcessFileName !in~ ("explorer.exe", "csrss.exe", "dwm.exe", "winlogon.exe", "taskhost.exe", "taskhostw.exe", "ShellExperienceHost.exe")
)
| sort by Timestamp descDetects Extra Window Memory injection by monitoring for suspicious API calls (SetWindowLong, SendMessage) targeting explorer.exe's Shell_TrayWnd window from non-Explorer processes. EWM injection specifically targets the Shell_TrayWnd extra window memory to store a pointer to injected code, then triggers execution via SendNotifyMessage. Also detects cross-process access to explorer.exe with write capabilities.
Data Sources
Required Tables
False Positives & Tuning
- Shell extensions and explorer plugins that legitimately modify Shell_TrayWnd properties
- Taskbar customization tools (StartAllBack, Start11) modifying Shell_TrayWnd EWM
- Accessibility tools that modify window properties for screen reading
- System tray management applications interacting with Shell_TrayWnd
Other platforms for T1055.011
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Enumerate Shell_TrayWnd Window Handle
Expected signal: Sysmon Event ID 1: PowerShell execution with FindWindowW in command line. API call to FindWindowW with class name Shell_TrayWnd logged by ETW if user32.dll API tracing is enabled.
- Test 2GetWindowLong Extra Memory Read
Expected signal: Sysmon Event ID 1: PowerShell execution with GetWindowLongPtrW. ETW: user32.dll API calls for FindWindowW and GetWindowLongPtrW.
- Test 3Cross-Process Memory Write to Explorer
Expected signal: Sysmon Event ID 1: PowerShell execution. If actual OpenProcess with write rights is called: Sysmon Event ID 10 (ProcessAccess) from PowerShell to explorer.exe with PROCESS_VM_WRITE.
References (5)
- https://attack.mitre.org/techniques/T1055/011/
- https://www.malwaretech.com/2013/08/powerloader-injection-something-truly.html
- https://www.welivesecurity.com/2013/03/19/gapz-and-redyms-droppers-based-on-power-loader-code/
- https://www.endgame.com/blog/technical-blog/ten-process-injection-techniques-technical-survey-common-and-trending-process
- https://msdn.microsoft.com/library/windows/desktop/ms633591.aspx
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