plone.app.portlets vulnerable to denial of service via RSS feed portlet

Impact

By adding an RSS portlet, and giving this a link to a very large file, a member can cause a denial of service attack, because Plone will use lots of memory. The member could also use different urls to try to get information about the internal network and open port numbers (SSRF). A malicious RSS feed could cause stored XSS, when the url of a feed item is a javascript url.

Patches

The problem has been patched in plone.app.portlets.

• For Plone 6.2: upgrade to plone.app.portlets 7.0.2
• For Plone 6.1: upgrade to plone.app.portlets 6.0.4
• For Plone 6.0: upgrade to plone.app.portlets 5.0.8

Workarounds

If upgrading is not immediately possible:

• Restrict who can manage portlets: remove the plone.app.portlets.ManageOwnPortlets permission from untrusted roles, and limit Manage portlets to trusted administrators (usually this is already restricted to the Manager and Site Administrator roles).
• Where the RSS portlet is not needed, unregister it so it cannot be added. This would need to be done by editing a portlets.xml in your own code, so it is not a quick fix.

References

This is similar to this plone.app.event vulnerability. It was discovered by the Plone Security Team by thinking of similar cases to the plone.app.event problem.