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Simple Buffer Overflow Example

Simple Buffer Overflow Example. Dan Fleck CS469 Security Engineering Reference: http:// www.thegeekstuff.com /2013/06/buffer-overflow/ . 1. 1. Buffer Overflows. Buffer overflows occur when some sized portion of memory is overwritten with something bigger. For example:

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Simple Buffer Overflow Example

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  1. Simple Buffer Overflow Example Dan Fleck CS469 Security Engineering Reference: http://www.thegeekstuff.com/2013/06/buffer-overflow/ 1 1 Coming up: Buffer Overflows

  2. Buffer Overflows • Buffer overflows occur when some sized portion of memory is overwritten with something bigger. • For example: • char buff[10]; // Min index is 0, max index is ???? • Overflow: • buff[10] =‘d’; 2 Coming up: Why care?

  3. Why care? • Minimally buffer overflows can cause program crashes or unexpected results • char *ptr = (char *) malloc (10); // Allocate 10 bytes on heap ptr[10] = ‘d’ ; // Crash! • However because buffer overflows corrupt memory nearby the variable being over-filled, an informed hacker can use this to write data into other protected areas of the program (i.e. stack and heap) • char buff[10] = {0}; strcpy(buff, “Lets overflow that buffer!”); // Stack overflow! 3 Coming up: An attack

  4. An attack intmain(void) { char buff[15]; int pass = 0; printf("\n Enter the password : \n"); gets(buff); // Get the password from the user if(strcmp(buff, "thegeekstuff")) { // Check the password printf ("\n Wrong Password \n"); } else { printf ("\n Correct Password \n"); pass = 1; // Set a flag denoting correct pass } if(pass) { /* Now Give root or admin rights to user*/ printf("\n Root privileges given to the user \n"); } return 0; } 4 Lets test it! Coming up: Lets look inside…

  5. Lets look inside… • GDB is a common debugger for C programs. • gcc –g myFile.c // -g option enables debug symbols and thus debugging • DDD is a graphical front-end to GDB. Typically GDB is used from a command line interface 5 Coming up: Lessons

  6. Lessons • Buffer overflows occur when memory bounds of a variable are exceeded • They can occur on the heap or the stack • Buffer overflows have unintended consequences. • There are protections against unsafe operations however they may not always be used (or known) 35 6 Coming up: References

  7. References • http://blog.zynamics.com/2010/03/12/a-gentle-introduction-to-return-oriented-programming/ • http://cseweb.ucsd.edu/~hovav/dist/geometry.pdf • Stealth: http://www.suse.de/~krahmer/no-nx.pdf • Nergel, http://www.phrack.com/issues.html?issue=58&id=4#article • http://cseweb.ucsd.edu/~hovav/dist/rop.pdf 36 36 7 End of presentation

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