Source: http://packetstormsecurity.org/files/view/99362/b2evolution403-xss.txt

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Software................b2evolution 4.0.3
Vulnerability...........Persistent Cross-site Scripting
Threat Level............Moderate (2/5)
Download................http://b2evolution.net/
Vendor Contact Date.....3/15/2011
Disclosure Date.........3/15/2011
Tested On...............Windows Vista + XAMPP
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Author..................AutoSec Tools
Site....................http://www.autosectools.com/
Email...................John Leitch <john@autosectools.com>
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--Description--

A persistent cross-site scripting vulnerability in b2evolution 4.0.3
can be exploited to execute arbitrary JavaScript.


--Exploit--

Data submitted to the "Comment text" input of the blog comment form is
not properly santized. As a result, javascript can be executed
throughout the application (admin dashboard, admin comment full text
view, possibly other pages).


--PoC--

<?<a><script>alert(0)</script>