Type Confusion Vulnerabilities

Today, we are going to explore a new vulnerability called “Type Confusion” and as the name indicates this is a logical bug which results from a confusion between object types.

First we need to know about C++ Casting operations and there are 3 main types of them.

C++ Casting Operations:

1- Static Casting –> static_cast<ToClass>(Object)

  • Class hierarchy check at compile time

2- Dynamic Casting –> dynamic_cast<ToClass>(Object)

  • Run-time check based on allocated type (vtable pointer)
  • Not used in performance critical code

3- C-style Casting –> (ToClass) (Object)

  • C-style cast, no check for the object type at all

Type Confusion bugs arises from illegal down-casts

Casting Types

Up-casting (Widening):

  • Cast subclass to base class
  • Done automatically

Down-casting (Narrowing):

  • Cast base class to subclass
  • Need explicit cast
Child1 *c = new Child1();
Parent *p = static_cast<Parent*>(c); //Up-casting
Child2 *d = static_cast<Child2*>(p); //Down-casting

How can we exploit type confusion bugs?

Fundamentally we need to control two pointers of different types to the same memory area

Simple Exploitation Demo

#include <iostream>
using namespace std;

class Base {}; // Parent Class

class Execute: public Base {   // Child of Base Class
	virtual void exec(const char *program) 

class Greeter: public Base {   // Child of Base Class
	virtual void sayHi(const char *str) 
		cout << str << endl;


int main() {

	Base *b1 = new Greeter();
	Base *b2 = new Execute();
	Greeter *g;

	g = static_cast<Greeter*>(b1); // Safe Casting to the same type "Greeter"
	g->sayHi("Greeter says hi!"); // String passed to sayHi() function

	g = static_cast<Greeter*>(b2); // Unsafe Casting to sibling class "Execute"
	g->sayHi("/usr/bin/xcalc"); // String passed to exec() function 
                                    // which will turn into a command to execute calculator

	delete b1;
	delete b2;
	return 0;

Let’s compile this simple c++ program and run it

g++ typeConfusion_Example.cpp -o typeConfusion_Example

And boom you got a command execution!


Leave a Reply