dnpatch

[WIP] .NET Patcher library using dnlib.

If you have questions feel free to ask me via Gitter! I'm glad to help you out!

[] (https://github.com/ioncodes/dnpatch/releases)

Patching

The constructor takes the filename of the assembly.

Patcher patcher = new Patcher("Test.exe");

Targeting Methods

All methods take an object called Target as argument. The object is defined as follows:

public string Namespace { get; set; } // needed
public string Class { get; set; } // needed
public string Method { get; set; } // needed

/* If you want to patch multiple indexes in the method */
public int[] Indexes { get; set; }
public Instruction[] Instructions { get; set; }

/* If you want to patch 1 index in the method */
public int Index { get; set; } = -1;
public Instruction Instruction { get; set; }

/* If the path to the method has more than 1 nested class use this */
public string[] NestedClasses { get; set; }

/* If the path to the method has 1 nested class use this */
public string NestedClass { get; set; }

Please make sure that you don't assign inconsistent values, e.g.

var target = new Target
{
    Instructions = ...
    Instruction = ...
}

If you want to patch multiple methods create a Target[] and pass it to the functions, it is accepted by the most of them.

Creating Instructions

Reference dnlib and create an Instruction[] or Instruction with your Instruction(s) and assign Indexes (int[]) or Index with the indexes where the Instructions are. You can find them by reverse engineering your assembly via dnSpy or some other decompiler.

Small Example:

Instruction[] opCodes = {
    Instruction.Create(OpCodes.Ldstr, "Hello Sir 1"),
    Instruction.Create(OpCodes.Ldstr, "Hello Sir 2")
};
int[] indexes = {
    0, // index of Instruction
    2
};
Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "Print",
    Instructions = opCodes,
    Indexes = indexes
};

Patch the whole methodbody

To clear the whole methodbody and write your instructions, make sure that you don't assign the Indexes or Index property.

Here is an example:

Instruction[] opCodes = {
    Instruction.Create(OpCodes.Ldstr, "Hello Sir"), // String to print
    Instruction.Create(OpCodes.Call, p.BuildMemberRef("System", "Console", "WriteLine")), // Console.WriteLine call -> BUILDMEMBERREF IS ONLY FOR CONSOLE.WRITELINE
    Instruction.Create(OpCodes.Ret) // Alaway return smth
};
Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "Print",
    Instructions = opCodes
};

Apply the patch

To apply your modified instructions you can call the method 'Patch':

patcher.Patch(Target);

or

patcher.Patch(Target[]);

Finding an instruction

In some cases it might be useful to have find an instruction within a method, for example if the method got updated.

Instruction opCode = Instruction.Create(OpCodes.Ldstr, "TheTrain");
Instruction toFind = Instruction.Create(OpCodes.Ldstr, "TheWord");
Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "FindMe",
    Instruction = opCode // you can also set it later
};
target.Index = p.FindInstruction(target, toFind);
// now you have the full Target object

Let's say there are multiple identical instructions. What now, baoss? Well, it's simple. There's an overload that takes and int which is the occurence of the instruction which you'd like to find.

Instruction opCode = Instruction.Create(OpCodes.Ldstr, "TheTrain");
Instruction toFind = Instruction.Create(OpCodes.Ldstr, "TheWord");
Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "FindMe",
    Instruction = opCode // you can also set it later
};
target.Index = p.FindInstruction(target, toFind, 2); // Sir, find the second occurence!

Replacing instructions

In some cases it might be easier to just replace an instruction. At this point of development, it doesn't make much sense, but the features will come soon.

Instruction opCode = Instruction.Create(OpCodes.Ldstr, "I love kittens");
Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "ReplaceMe",
    Instruction = opCode,
    Index = 0
};
p.ReplaceInstruction(target);

Removing instructions

Let's say you want to remove instructions... Well it's simple as this:

Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "RemoveMe",
    Indexes = new[]{0,1} // the indexes, you can also just use 'Index'
};
p.RemoveInstruction(target);

Patching operands

Hmmm.... What if you find the console output offending? You can modify the Ldstr without even creating an instruction :)

Target target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "PrintAlot",
    Index = 0
};
p.PatchOperand(target, "PatchedOperand"); // pass the Target and a string to replace

or incase you need to modify an int:

p.PatchOperand(target, 1337);

It is also able to patch multiple operands in the same method by using int[] or string[].

Returning true/false

If you want to overwrite the methodbody with a return true/false statement you can do this:

target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "VerifyMe"
};
p.WriteReturnBody(target, bool); // bool represents the return value

Clearing methodbodies

If you just want to empty a methodbody, use this amigo:

target = new Target()
{
    Namespace = "Test",
    Class = "Program",
    Method = "WriteLog"
};
p.WriteEmptyBody(target);

Building calls

To build calls like "Console.WriteLine()" you can use this method:

p.BuildMemberRef(string, string, string, Patcher.MemberRefType);
/* 
 * string 1 -> namespace, e.g. "System"
 * string 2 -> class, e.g. "Console"
 * string 3 -> method, e.g. "WriteLine"
 * MemberRefType -> the reference type, e.g. Static
 */

MemberRefType is defined as follows:

public enum MemberRefType
{
    Static,
    Instance
}

Here is an IL example for Console.WriteLine:

Instruction.Create(OpCodes.Call, p.BuildMemberRef("System", "Console", "WriteLine", Patcher.MemberRefType.Static));

Saving the patched assembly

If you want to safe the assembly under a different name use this:

patcher.Save(String); // filename here

Or if you want to replace the original file:

patcher.Save(bool); // if true it will create a backup first (filename.bak)

Obfuscated assemblies...

This part is in heavy development right now. The main purpose is to find a method and patch the instructions without the need of knowing the names incase the namespaces, etc are renamed via an obfuscator.

Constructor

Create an Object called 'ObfuscationPatcher':

var op = new ObfuscationPatcher(string, bool);
// string: filename
// bool: keep old max stack?

Searching the target method

By operand

Let's say the strings are not encrypted (I'm talking about Ldstr here):

string[] operands = {
    "Find",
    "TheWord",
    "The",
    "Word",
    "You",
    "Wont"
}; // Find there words within the method.
Target[] obfuscatedTargets = op.FindInstructionsByOperand(operands); // let the boi work. It will return an Target[] with all methods he could find.
foreach (var obfTarget in obfuscatedTargets) // Let's iterate and have fun
{
    obfTarget.Instructions = new Instruction[]
    {
        Instruction.Create(OpCodes.Ldstr, "Obfuscator"),
        Instruction.Create(OpCodes.Ldstr, "Got"),
        Instruction.Create(OpCodes.Ldstr, "Rekt"),
        Instruction.Create(OpCodes.Ldstr, "Hell"),
        Instruction.Create(OpCodes.Ldstr, "Yeah"),
        Instruction.Create(OpCodes.Ldstr, "!")
    }; // modify the instructions
}
op.Patch(obfuscatedTargets); // Patch the instructions

By OpCode

Let's say you look for an OpCode, you can do this:

op.FindInstructionsByOpcode(new[] {OpCodes.Add}) // NOT TESTED

Patching

As before you will just do this:

op.Patch(Target); // Patch the instructions
// or
op.Patch(Target[]); // Patch multiple targets

Save the assembly

Again, as before :)

op.Save(string); // string -> filename

Resources

Wanna patch some resources? No, problem! Just create an object called ResourcePatcher!

ResourcePatcher rp = new ResourcePatcher(string); // string-> assembly

Insert resources

Add resources using this piece of code:

rp.InsertResource(string, byte[]);
/*
 * string -> resourcename
 * byte[] -> ByteArray of the data to write
 */

You can replace byte[] with a string to load the byte[] from a file.

Removing resources

You can remove resources if you know the index:

rp.RemoveResource(int); // int -> index

If you want to remove all resources do this:

rp.RemoveResources();

Replacing resources

If you want to replace a resource, you can do this my friend:

rp.ReplaceResource(int, string, byte[]);
/*
 * int -> index
 * string -> name
 * byte[] -> ByteArray with your data
 */

You can replace byte[] with a string pointing to a file.

Getting resources

dnlib stores the resources as ResourceCollection and I'm not going to wrap it, use this method to get the resources:

rp.GetResources();

Save

As always:

rp.Save(string);
// or
rp.Save(bool);

Credits

I'd like to thank these people:

• 0xd4d for creating dnlib