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Fix .NET Reactor method decryption #26

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Merged
meck-gd merged 6 commits into from
Apr 22, 2026
Merged

Fix .NET Reactor method decryption #26

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1615fb8
.NET Reactor: Only remove method decrypt calls when option is enabled
meck-gd Apr 15, 2026
1934112
InstructionEmulator: Don't handle bogus array sizes
meck-gd Apr 16, 2026
6d03925
.NET Reactor: Unify FindStartEnd and GetLocal methods in EncryptedRes…
meck-gd Apr 17, 2026
e6591fe
.NET Reactor: Fix MethodsDecrypter for newer versions
meck-gd Apr 17, 2026
23b7da0
.NET Reactor: Fix resource decryption if they're not compressed
meck-gd Apr 20, 2026
1723a40
.NET Reactor: Fix detection of ldtoken virtual opcode in some cases
meck-gd Apr 22, 2026
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3 changes: 1 addition & 2 deletions de4dot.blocks/cflow/InstructionEmulator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -532,9 +532,8 @@ void Emulate_Sizeof(Instruction instr){
void Emulate_Newarr(Instruction instr)
{
var val = valueStack.Pop();
if (val.IsInt32())
if (val.IsInt32() && val is Int32Value { Value: < 500000 } arrSize)
{
Int32Value arrSize = (Int32Value)val;
List<Value> arr = new List<Value>(arrSize.Value);
for (int i = 0; i < arrSize.Value; i++) {
arr.Add(new UnknownValue());
Expand Down
7 changes: 4 additions & 3 deletions de4dot.code/deobfuscators/dotNET_Reactor/v4/Deobfuscator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -446,7 +446,8 @@ public override IDeobfuscator ModuleReloaded(ModuleDefMD module) {
newOne.peImage = new MyPEImage(fileData);
newOne.methodsDecrypter = new MethodsDecrypter(module, methodsDecrypter);
newOne.proxyCallFixer = new ProxyCallFixer(module, proxyCallFixer);
newOne.devirtualizer = new Devirtualizer(module, devirtualizer);
newOne.devirtualizer = new Devirtualizer(DeobfuscatedFile, module);
newOne.devirtualizer.Find();
newOne.stringDecrypter = new StringDecrypter(module, stringDecrypter);
newOne.booleanDecrypter = new BooleanDecrypter(module, booleanDecrypter);
newOne.assemblyResolver = new AssemblyResolver(module, assemblyResolver);
Expand All @@ -462,7 +463,7 @@ void FreePEImage() {
}

void RemoveMethods() {
if (methodsDecrypter.Method != null) {
if (methodsDecrypter.Method != null && options.DecryptMethods) {
AddEntryPointCallToBeRemoved(methodsDecrypter.Method);
}

Expand Down Expand Up @@ -501,7 +502,7 @@ void RemoveMethods() {
if (antiDebug != null)
AddCallToBeRemoved(method, antiDebug);

if (methodsDecrypter.Method != null)
if (methodsDecrypter.Method != null && options.DecryptMethods)
AddCallToBeRemoved(method, methodsDecrypter.Method);

// AntiILDASM
Expand Down
234 changes: 64 additions & 170 deletions de4dot.code/deobfuscators/dotNET_Reactor/v4/EncryptedResource.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -237,13 +237,69 @@ public byte[] Encrypt(byte[] data) {
}
}

class DecrypterV2 : IDecrypter {
private abstract class EmulatingDecrypterBase
{
protected MethodDef method;
protected List<Instruction> instructions;
protected List<Local> locals;
protected readonly InstructionEmulator instrEmulator = new();
protected Local emuLocal;

/**
* Locates the instructions that are responsible for producing the key stream for decrypting the resource.
*/
protected bool FindStartEnd(IList<Instruction> instrs, out int startIndex, out int endIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_R_Un)
continue;
if (instrs[i + 1].OpCode.Code != Code.Conv_R8)
continue;
if (instrs[i + 2].OpCode.Code != Code.Conv_U4)
continue;
if (instrs[i + 3].OpCode.Code != Code.Add)
continue;
int newEndIndex = i + 3;
int newStartIndex = -1;
for (int j = newEndIndex; j >= 0; j--) {
// Search upwards for array access or br.
if (instrs[j].OpCode.Code != Code.Ldelem_U1 && (!instrs[j].IsBr() || instrs[j - 1].OpCode.Code == Code.Bne_Un_S))
continue;

// Go down to next local load, where the actual decryption should begin.
for (int k = j + 1; k < newEndIndex; k++) {
if (instrs[k].IsLdloc()) {
newStartIndex = k;
break;
}
}
break;
}
endIndex = newEndIndex;
startIndex = newStartIndex;
tmpLocal = CheckLocal(instrs[startIndex], true);
return true;
}
endIndex = 0;
startIndex = 0;
tmpLocal = null;
return false;
}

/**
* Gets the Local referenced by the instruction if it's either ldloc or stloc (determined by isLdloc).
*/
protected Local CheckLocal(Instruction instr, bool isLdloc) {
if (isLdloc && !instr.IsLdloc())
return null;
if (!isLdloc && !instr.IsStloc())
return null;

return instr.GetLocal(locals);
}
}

class DecrypterV2 : EmulatingDecrypterBase, IDecrypter {
readonly byte[] key, iv;
MethodDef method;
List<Instruction> instructions;
List<Local> locals;
readonly InstructionEmulator instrEmulator = new InstructionEmulator();
Local emuLocal;
Parameter emuArg;
MethodDef emuMethod;
bool isNewDecrypter;
Expand Down Expand Up @@ -310,49 +366,6 @@ bool Find(IList<Instruction> instrs, out int startIndex, out int endIndex, out L
return true;
}

bool FindStartEnd(IList<Instruction> instrs, out int startIndex, out int endIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_R_Un)
continue;
if (instrs[i + 1].OpCode.Code != Code.Conv_R8)
continue;
if (instrs[i + 2].OpCode.Code != Code.Conv_U4)
continue;
if (instrs[i + 3].OpCode.Code != Code.Add)
continue;
int newEndIndex = i + 3;
int newStartIndex = -1;
for (int x = newEndIndex; x > 0; x--)
if (instrs[x].OpCode.FlowControl != FlowControl.Next) {
newStartIndex = x + 1;
break;
}
if (newStartIndex < 0)
continue;

var checkLocs = new List<Local>();
int ckStartIndex = -1;
for (int y = newEndIndex; y >= newStartIndex; y--) {
var loc = CheckLocal(instrs[y], true);
if (loc == null)
continue;
if (!checkLocs.Contains(loc))
checkLocs.Add(loc);
if (checkLocs.Count == 3)
break;
ckStartIndex = y;
}
endIndex = newEndIndex;
startIndex = Math.Max(ckStartIndex, newStartIndex);
tmpLocal = CheckLocal(instrs[startIndex], true);
return true;
}
endIndex = 0;
startIndex = 0;
tmpLocal = null;
return false;
}

bool FindStartEnd2(ref IList<Instruction> instrs, out int startIndex, out int endIndex, out Local tmpLocal, out Parameter tmpArg, ref MethodDef methodDef, ref List<Local> locals) {
foreach (var instr in instrs) {
if (instr.OpCode == OpCodes.Call) {
Expand Down Expand Up @@ -436,15 +449,6 @@ bool FindEnd(IList<Instruction> instrs, int startIndex, out int endIndex) {
return false;
}

Local CheckLocal(Instruction instr, bool isLdloc) {
if (isLdloc && !instr.IsLdloc())
return null;
else if (!isLdloc && !instr.IsStloc())
return null;

return instr.GetLocal(locals);
}

public byte[] Decrypt(EmbeddedResource resource) {
var encrypted = resource.CreateReader().ToArray();
var decrypted = new byte[encrypted.Length];
Expand Down Expand Up @@ -517,13 +521,7 @@ public byte[] Encrypt(byte[] data) {
}
}

class DecrypterV3 : IDecrypter {
readonly MethodDef method;
List<Instruction> instructions;
readonly List<Local> locals;
readonly InstructionEmulator instrEmulator = new InstructionEmulator();
Local emuLocal;

class DecrypterV3 : EmulatingDecrypterBase, IDecrypter {
public DnrDecrypterType DecrypterType => DnrDecrypterType.V3;

public DecrypterV3(MethodDef method) {
Expand Down Expand Up @@ -578,48 +576,6 @@ bool Find(IList<Instruction> instrs, out int startIndex, out int endIndex, out L
return true;
}

/**
* Locates the instructions that are responsible for producing the key stream for decrypting the resource.
*/
bool FindStartEnd(IList<Instruction> instrs, out int startIndex, out int endIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_R_Un)
continue;
if (instrs[i + 1].OpCode.Code != Code.Conv_R8)
continue;
if (instrs[i + 2].OpCode.Code != Code.Conv_U4)
continue;
if (instrs[i + 3].OpCode.Code != Code.Add)
continue;
int newEndIndex = i + 3;

int newStartIndex = -1;
for (int j = newEndIndex; j >= 0; j--) {
// Search upwards for array access.
if (instrs[j].OpCode.Code != Code.Ldelem_U1)
continue;

// Go down to next local load, where actual decryption should begin.
for (int k = j + 1; k < newEndIndex; k++) {
if (instrs[k].IsLdloc()) {
newStartIndex = k;
break;
}
}
break;
}

endIndex = newEndIndex;
startIndex = newStartIndex;
tmpLocal = CheckLocal(instrs[startIndex], true);
return true;
}
endIndex = 0;
startIndex = 0;
tmpLocal = null;
return false;
}

bool FindStart(IList<Instruction> instrs, out int startIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_U)
Expand Down Expand Up @@ -675,18 +631,6 @@ bool FindEnd(IList<Instruction> instrs, int startIndex, out int endIndex) {
return false;
}

/**
* Gets the Local referenced by the instruction if it's either ldloc or stloc (determined by isLdloc).
*/
Local CheckLocal(Instruction instr, bool isLdloc) {
if (isLdloc && !instr.IsLdloc())
return null;
if (!isLdloc && !instr.IsStloc())
return null;

return instr.GetLocal(locals);
}

public byte[] Decrypt(EmbeddedResource resource) {
var encrypted = resource.CreateReader().ToArray();
var decrypted = new byte[encrypted.Length];
Expand Down Expand Up @@ -766,14 +710,10 @@ public byte[] Encrypt(byte[] data) {
}
}

class DecrypterV4 : IDecrypter {
class DecrypterV4 : EmulatingDecrypterBase, IDecrypter {
readonly byte[] key, iv;
MethodDef decryptMethod;
MethodDef emuMethod;
List<Instruction> instructions;
List<Local> locals;
readonly InstructionEmulator instrEmulator = new InstructionEmulator();
Local emuLocal;

public DnrDecrypterType DecrypterType => DnrDecrypterType.V4;

Expand Down Expand Up @@ -908,43 +848,6 @@ bool Find(IList<Instruction> instrs, out int startIndex, out int endIndex, out L
return true;
}

bool FindStartEnd(IList<Instruction> instrs, out int startIndex, out int endIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_R_Un)
continue;
if (instrs[i + 1].OpCode.Code != Code.Conv_R8)
continue;
if (instrs[i + 2].OpCode.Code != Code.Conv_U4)
continue;
if (instrs[i + 3].OpCode.Code != Code.Add)
continue;
int newEndIndex = i + 3;
int newStartIndex = -1;
for (int j = newEndIndex; j >= 0; j--) {
// Search upwards for array access.
if (instrs[j].OpCode.Code != Code.Ldelem_U1)
continue;

// Go down to next local load, where actual decryption should begin.
for (int k = j + 1; k < newEndIndex; k++) {
if (instrs[k].IsLdloc()) {
newStartIndex = k;
break;
}
}
break;
}
endIndex = newEndIndex;
startIndex = newStartIndex;
tmpLocal = CheckLocal(instrs[startIndex], true);
return true;
}
endIndex = 0;
startIndex = 0;
tmpLocal = null;
return false;
}

bool FindStart(IList<Instruction> instrs, out int startIndex, out Local tmpLocal) {
for (int i = 0; i + 8 < instrs.Count; i++) {
if (instrs[i].OpCode.Code != Code.Conv_U)
Expand Down Expand Up @@ -1000,15 +903,6 @@ bool FindEnd(IList<Instruction> instrs, int startIndex, out int endIndex) {
return false;
}

Local CheckLocal(Instruction instr, bool isLdloc) {
if (isLdloc && !instr.IsLdloc())
return null;
else if (!isLdloc && !instr.IsStloc())
return null;

return instr.GetLocal(locals);
}

public byte[] Decrypt(EmbeddedResource resource) {
var encrypted = resource.CreateReader().ToArray();
var decrypted = new byte[encrypted.Length];
Expand Down
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