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“Couple of other techniques in fact the next one we re going to ntalked about about is hardly used a number of operating systems. Now and so none thing that going to be different about the next. Two techniques. We ll ntalked about is that they going to use support from the operating nsystem hardware.
That we have to deal with buffer overflow or nto. Thwart buffer overflow attacks. So the first one as which i nsaid. Many operating systems use is what is called naddress space.
Layout..
Randomization aslr. So remember. In an address space. Some place stack nis space.
Where stack is allocated so stack starts at certain place somewhere. The library code goes another nplace where the heap goes. And so on what if we randomize the places nwhere these areas of memory. Start.
Remember that hacker had to actually nguess where key information is so if i wanted to do return to libc nattack..
I had to know where the library is where a certain function may be so ni. Know the address of that function. And i can use that as i overflow the nreturn address field in the stack frame. So i need to know these address and what aslr does it makes hard nbecause of the randomization that we do it makes hard for the attacker to nfind these important locations where the address that nthe attacker is interested in is going to over the information address of the information that that nhacker is interested in is not know so as i said a number of operating systems nthese days.
Actually do that to protect the programs and processes from nthese buffer overflow kind of attacks. So this just makes it harder for the nhacker to successfully craft an attack where can return or manage or direct ncontrol of the program to the certain known place that could be used to let nthe attacker execute arbitrary code this one other defense against nstack buffer overflow when the shell code itself nis stored on the stack. So remember if i don t do return nto libc. Then my return address has to point me to some place where nthe shell code lives or is stored and you could write that shell code ninto some area of the stack itself and then you can execute off the stack.
There s no legitimate reason for us to execute instructions nthat are stored on the stack..
So one thing. We can do is we can nmake the stack non executable basically says the system is nnot going to allow you to fetch instructions from the stack area or nthe stack segment. If you do that then you ncan t execute on the stack. So your shell code ncannot be on the stack you have to find some other place to put nyour shell code.
And maybe. That s why you have to try tricks like return. Nto libc and things like that and use a library function nto transfer control to the code that attacker ones. Executed.
So here..
I guess we talked about sort nof security is increasing assurance making the attacker s njob. More difficult and making the legitimate in this ncase here. We re talking programmers their task somewhat easier so aslr obviously is making nthe attackers job more difficult because key addresses that they need to know they don t know exactly where nthey are in the address space. And they can t put code on the stack and hope to get it executed.
Because we have nthe hardware operating system says not supposed to fetch instructions from nthe stack area of the address space. So these are techniques for nactually dealing with buffer overflows as we said one makes it harder for nthe attacker by making it difficult for ” ..
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