DrSemu

Dr.Semu

Dr.Semu runs executables in an isolated environment, monitors the behavior of a process, and based on Dr.Semu rules created by you or the community, detects if the process is malicious or not.

[The tool is in the early development stage]

whoami: @_qaz_qaz

With Dr.Semu you can create rules to detect malware based on dynamic behavior of a process.

Isolation through redirection

Everything happens from the user-mode. Windows Projected File System (ProjFS) is used to provide a virtual file system. For Registry redirection, it clones all Registry hives to a new location and redirects all Registry accesses.

See the source code for more about other redirections (process/objects isolation, etc).

Monitoring

Dr.Semu uses DynamoRIO (Dynamic Instrumentation Tool Platform) to intercept a thread when it's about to cross the user-kernel line. It has the same effect as hooking SSDT but from the user-mode and without hooking anything.

At this phase, Dr.Semu produces a JSON file, which contains information from the interception.

Detection

After terminating the process, based on Dr.Semu rules we receive if the executable is detected as malware or not.

Dr.Semu Rules/Detections

Dr.Semu rules

They are written in Python or LUA (located under dr_rules) and use dynamic information from the interception and static information about the sample. It's trivial to add support of other languages.

Example (Python): https://gist.github.com/secrary/ac89321b8a7bde998a6e3139be49eb72

Example (Lua): https://gist.github.com/secrary/e16daf698d466136229dc417d7dbcfa3

Usage

• Use PowerShell to enable ProjFS in an elevated PowerShell window:

Enable-WindowsOptionalFeature -Online -FeatureName Client-ProjFS -NoRestart

• Download and extract a zip file from the releases page

• Download DynamoRIO and extract into DrSemu folder and rename to dynamorio

• Install Python 3 x64

DrSemu.exe --target file_path

DrSemu.exe --target files_directory

DEMO

BUILD

• Use PowerShell to enable ProjFS in an elevated PowerShell window:

Enable-WindowsOptionalFeature -Online -FeatureName Client-ProjFS -NoRestart

• Install Python 3 x64

• Download DynamoRIO and extract into bin folder and rename to dynamorio

• Build pe-parser-library.lib library:

  • Generate VS project from DrSemushared_libspe_parse using cmake-gui
  • Build 32-bit library under build (shared_libspe_parsebuildpe-parser-libraryRelease) and 64-bit one under build64
  • Change run-time library option to Multi-threaded (/MT)

• Set LauncherCLI As StartUp Project

TODO

• Solve isolation related issues
• Improve synchronization
• Update the description, add more details
• Create a GUI for the tool

Limitations

• Minimum supported Windows version: Windows 10, version 1809 (due to Windows Projected File System)
• Maximum supported Windows version: Windows 10, version 1809 (DynamoRIO supports Windows 10 versions until 1809)