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C# Detect if Debugger is Attached

, 19 Oct 2013
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C# detect if debugger is attached

This method is used to detect if a running process has a debugger attached to it. It involves using CheckRemoteDebuggerPresent, imported from kernel32.dll via PInvoke.

* tested on Visual Studio's Debugger & OllyDbg

How To...

First, include the following two lines in your program (which will import CheckRemoteDebuggerPresent):

[DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
static extern bool CheckRemoteDebuggerPresent(IntPtr hProcess, ref bool isDebuggerPresent);

Now, this method is pretty simple to use since it takes only 2 arguments:

  1. IntPtr hProcess = the target process' handle
  2. ref bool isDebuggerPresent = pointer that indicates the result

This method does all the 'hard work', so no further code is required: 

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

public class DetectDebugger
{
    [DllImport("kernel32.dll", SetLastError = true, ExactSpelling = true)]
    static extern bool CheckRemoteDebuggerPresent(IntPtr hProcess, ref bool isDebuggerPresent);

    public static void Main()
    {
        bool isDebuggerPresent = false;
        CheckRemoteDebuggerPresent(Process.GetCurrentProcess().Handle, ref isDebuggerPresent);

        Console.WriteLine("Debugger Attached: " + isDebuggerPresent);
        Console.ReadLine();
    }
}

Update

In order to avoid any confusion about Debugger.IsAttached and IsDebuggerPresent - sorry I didn't mention this earlier in the tip:

  • IsDebuggerPresent = works for any running process and detects native debuggers too
  • Debugger.IsAttached = works only for the current process and detects only managed debuggers. OllyDbg won't be detected by this.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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Apex95

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Comments and Discussions

 
GeneralMy vote of 3 PinmemberFlorian Rosmann17-Oct-13 22:27 
GeneralRe: My vote of 3 PinmemberApex9518-Oct-13 1:24 
GeneralRe: My vote of 3 PinmemberDan Colasanti18-Oct-13 3:01 
You should update your article with this information because it's not obvious and most devs won't read the comment responses to find it here.
 
I also suggest removing the line "It's a neat way to add a little bit of protection to your program, but don't expect too much since .NET is far from being safe", because there's nothing inherently unsafe about .NET - in fact, the opposite could easily be argued - that it's safer than native code because pointers to dynamically allocated objects are managed by the framework. In any case, I'm not sure how safety relates to checking whether a debugger is present/attached - if you are trying to make that point, it's not clear, so you may want to be more clear there.
 
You may also want to address the issue of the need for checking if the debugger is present in the first place (for example, many devs will argue that just calling System.Diagnostics.Debug.WriteLine does not need to have a IsDebuggerAttached conditional around it) and whether native debuggers like OllyDbg can have their calls stripped from a Release build like the VS debugger does (useful for minimizing Release build footprint & improving performance). I think that would add value to your article, since most .NET developers wouldn't know that about OllyDbg.
 
Good luck!
Dan
GeneralRe: My vote of 3 PinmemberGiuseppe Tollini19-Oct-13 1:12 
QuestionFor current process IsDebuggerPresent is enough PinmemberAnandChavali17-Oct-13 18:53 
GeneralThoughts PinprofessionalPIEBALDconsult17-Oct-13 18:28 

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