Reverse Engineering

dnSpy – NET Debugger & Assembly Editor

October 13, 2017
3 Min Read

Reverse Engineer .NET Assemblies

dnSpy is a tool to reverse engineer .NET assemblies. It includes a decompiler, a debugger and an assembly editor (and more) and can be easily extended by writing your own extension. It uses dnlib to read and write assemblies so it can handle obfuscated assemblies (eg. malware) without crashing.

 

NET Debugger & Assembly Editor: dnSpy

NET Debugger & Assembly Editor: dnSpy

Features (see below for more detail)

  • Debug .NET Framework and .NET Core assemblies, no source code required
  • Edit assemblies in C# or Visual Basic or IL, and edit all metadata
  • Light and dark themes
  • Extensible, write your own extension
  • High DPI support (per-monitor DPI aware)
  • And much more, see below

dnSpy uses the ILSpy decompiler engine and the Roslyn (C# / Visual Basic) compiler and many other open source libraries, see below for more info.

Debugger

  • Debug .NET Framework and .NET Core assemblies, no source code required
  • Set breakpoints and step into any assembly
  • Locals, watch, autos windows
  • Variables windows supports saving variables (eg. decrypted byte arrays) to disk or view them in the hex editor (memory window)
  • Object IDs
  • Multiple processes can be debugged at the same time
  • Break on module load
  • Tracepoints and conditional breakpoints
  • Export/import breakpoints and tracepoints
  • Call stack, threads, modules, processes windows
  • Break on thrown exceptions (1st chance)
  • Variables windows support evaluating C# / Visual Basic expressions
  • Dynamic modules can be debugged (but not dynamic methods due to CLR limitations)
  • Output window logs various debugging events, and it shows timestamps by default ????
  • Assemblies that decrypt themselves at runtime can be debugged, dnSpy will use the in-memory image. You can also force dnSpy to always use in-memory images instead of disk files.
  • Public API, you can write an extension or use the C# Interactive window to control the debugger

 

Assembly Editor

  • All metadata can be edited
  • Edit methods and classes in C# or Visual Basic with IntelliSense, no source code required
  • Add new methods, classes or members in C# or Visual Basic
  • IL editor for low level IL method body editing
  • Low level metadata tables can be edited. This uses the hex editor internally.

 

Hex Editor

  • Click on an address in the decompiled code to go to its IL code in the hex editor
  • Reverse of above, press F12 in an IL body in the hex editor to go to the decompiled code or other high level representation of the bits. It’s great to find out which statement a patch modified.
  • Highlights .NET metadata structures and PE structures
  • Tooltips shows more info about the selected .NET metadata / PE field
  • Go to position, file, RVA
  • Go to .NET metadata token, method body, #Blob / #Strings / #US heap offset or #GUID heap index
  • Follow references (Ctrl+F12)

Other

  • BAML decompiler
  • Blue, light and dark themes (and a dark high contrast theme)
  • Bookmarks
  • C# Interactive window can be used to script dnSpy
  • Search assemblies for classes, methods, strings etc
  • Analyze class and method usage, find callers etc
  • Multiple tabs and tab groups
  • References are highlighted, use Tab / Shift+Tab to move to next reference
  • Go to entry point and module initializer commands
  • Go to metadata token or metadata row commands
  • Code tooltips (C# and Visual Basic)
  • Export to project

 

List of other open source libraries used by dnSpy

  • ILSpy decompiler engine (C# and Visual Basic decompilers)
  • Roslyn (C# and Visual Basic compilers)
  • dnlib (.NET metadata reader/writer which can also read obfuscated assemblies)
  • VS MEF (Faster MEF equals faster startup)
  • ClrMD (Access to lower level debugging info not provided by the CorDebug API)

Download dnSpy

Tags