![]() #include Īt run-time, the contents of the argc and argv parameters, being parameters of the program, will be held in the kernel area. The program calls a function which allocates some memory onto the stack, copies a string from the command line into it and outputs the string with a welcome message. Let's take a look at a simple piece of C-code that does just this. This mechanism is where the trouble starts. With the parameters on the stack, the code of the function will then jump to somewhere else in memory and do something with these parameters. When the call is made, the parameters that are passed to the function, are pushed on top of the stack. Since the stack grows downward, every item pushed on top of the stack, will make it grow towards the low memory address area.Ĭonsider the case where a program calls a function, a piece of code that does something and returns where it was before. This stack area is where the magic happens. Note that the heap grows up (from low to higher memory) when more memory is required by an application and the stack grows downwards (from high to lower memory). When a new function is called, these are pushed on the end of the stack (see the stack abstract data type for more information on that). This holds the local variables for each of the functions. This is a big area of memory where large objects are allocated (like images, files, etc.)īelow the kernel is the stack. It is a read-only area, because these should not be allowed to be changed.Ībove the text is the data, where uninitialized and initialized variables are stored. The bottom area of the memory is called text and contains the actual code, the compiled machine instructions, of the program. The top of the memory is the kernel area, which contains the command-line parameters that are passed to the program and the environment variables. The operating system will effectively call the main method of the code as a function, which then starts the flow for the rest of the program. When a program is run by the operating system (OS), the executable will be held in memory in a very specific way that's consistent between different processes. In this article, I will focus on the core principle of buffer overflows. There are ways to bypass these measures, but that's a (more advanced) topic in itself. NOTE: For the purpose of this article and its examples, I have disabled protective measures, like Address Space Layout Randomization (ASLR), that may interfere with a clear demonstration of the buffer overflow issue. However, note that the issue applies to many different languages and operating systems. ![]() In this example we're using a C program in Linux. In order to understand how buffer overflows work, we need to understand what happens in memory when a program is run. A few examples are the PS2 Independence exploit, the Twilight Hack for the Wii or an iDevice Lock Activation Bypass on the iPad. By sending carefully crafted input to an application, an attacker can cause the application to execute arbitrary code, possibly taking over the machine.Īttackers have managed to identify buffer overflows in a many products and components. ![]() How does a typical buffer overflow exploit work in code, at run-time and in memory and what can be achieved by running it?Ī buffer overflow occurs when a program or process attempts to write more data to a fixed length block of memory (a buffer), than the buffer is allocated to hold.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |