Practicing buffer overflow attack in Ubuntu

Question

I am trying to learn to use buffer overflow attack in Ubuntu. Unfortunately, I cannot turn off Address Space Layout Randomization (ASLR) feature in this OS, which is turned on by default. I have tried some work around found in some fedora books:

echo "0" > /proc/sys/kernel/randomize_va_space

but for some reason the protection's still there. Please give me some suggestions. Thanks.

[edit]Actually the above command was not successful, it said "Permission Denied", even with sudo. How can I fix that?

[adding] I kept on getting segmetation fault error when it shows an address in stack. Is it related to non-executable stack in ubuntu :(?

Answer 1

You will need root perms before attempting it, and if I'm not mistaken, to restart once you've done it.

 sudo -i
 echo "0" > /proc/sys/kernel/randomize_va_space

Answer 2

gcc compile with -fno-stack-protector

Answer 3

to echo to files with root acces using sudo you can use the following code:

echo "0" | sudo tee /proc/sys/kernel/randomize_va_space

Answer 4

i have a similar problem. i did turn randomize_va_space to zero. also i compiled with -fno-stack-protector, but if i try to do the bof it says:

(gdb) run $(perl -e 'print "A"x320') Starting program: /home/server/bof $(perl -e 'print "A"x320') Programm started...

Program received signal SIGSEGV, Segmentation fault. 0x08048438 in vuln ()

but on a lower count of A's there will be:

(gdb) run $(perl -e 'print "A"x315') Starting program: /home/server/bof $(perl -e 'print "A"x315') Programm started...

Program received signal SIGSEGV, Segmentation fault. 0x00414141 in ?? ()

so only if i filled the whole eip with A's it will use a protection.

how can i disable this protection function?

Answer 5

found it myself

you have to compile this way:

gcc -fno-stack-protector -z execstack -o OUTPUT INPUT.c