Frame pointer overwriting and FreeBSD

From: chrisat_private
Date: Wed Jun 04 2003 - 06:32:23 PDT

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    Hi,
    
    Been trying some frame pointer overwriting techniques
    and it doesn't seem to be working like i'd expect on a
    FreeBSD (x86) system, wondering if the more familiar
    could clarify?
    
    I'm basically doing a frame pointer overwrite by 1 byte
    exploit.
    
    Stepping through the code in GDB i can make eip run
    into my NOPs, and then my shellcode, however, using
    (multiple) standard execve /bin/sh shellcodes written
    for FreeBSD, causes the vulnerable program to die with
    numerous errors like SIGFPE, SIGILL, etc (strangely
    enough, looking at what eip was in the core dump, it
    was usually in the string "/bin/sh").
    
    Is it correct that since i've altered ebp's value,  and
    as BSD passes it's arguments on the stack, i wont be
    able to get it working?
    
    I'm taking a guess that it works on Linux because it's
    syscall arguments get passed via registers?
    
    
    
    
    Cheers,
    
    Chris.
    



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