Cross-site Scripting and Open Redirect in plone.app.contenttypes
ImpactPlone is vulnerable to reflected cross site scripting and open redirect when an attacker can get a compromised version of the image_view_fullscreen page in a cache, for example in Varnish.
The technique is known as cache poisoning.
Any later visitor can get redirected when clicking on a link on this page.
Usually only anonymous users are affected, but this depends on your cache settings.PatchesNew versions of plone.app.contenttypes have been released.
Version 2.2.3 works on Plone 5.2 and will be included in Plone 5.2.7.
Version 3.0.0a9 works on Plone 6 and will be included in Plone 6.0.0a3.Note that the Products.CMFPlone package has the same problem in the 4.3 series.
In Plone 5.0-5.2, the default Products.ATContentTypes version has the same problem. See [advisory](https://github.com/plone/Products.ATContentTypes/security/advisories/GHSA-g4c2-ghfg-g5rh).
For all unpatched versions of the three packages, you can use the following workaround.WorkaroundMake sure the image_view_fullscreen page is not stored in the cache.
In Plone:Login as Manager and go to Site Setup.Go to the 'Caching' control panel. If this does not exist, or 'Enable caching' is not checked, you should normally not be vulnerable.Click on the tab 'Caching operations'.Under 'Legacy template mappings' locate the ruleset 'Content item view'.From the last column ('Templates')  remove 'image_view_fullscreen'.Click on Save.ReporterThis vulnerability was responsibly disclosed to the Plone Security Team by Gustav Hansen, F-Secure Consulting. Thank you!For more informationIf you have any questions or comments about this advisory, email us at [security@plone.org](mailto:security@plone.org)
This is also the correct address to use when you want to report a possible vulnerability.
See [our security report policy](https://plone.org/security/report).