Cross-site Scripting and Open Redirect in Products.CMFPlone

Summary

### Impact Plone 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.

### Patches No patch is available for the Products.CMFPlone 4 series. Versions 5.0 and higher are not affected, but two other packages used by these versions are affected.

`plone.app.contenttypes` has the same problem in all versions, see [advisory](https://github.com/plone/plone.app.contenttypes/security/advisories/GHSA-f7qw-5fgj-247x). 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). Plone 5.2.7 and 6.0.0a3 will be released today and will include these fixes.

For all unpatched versions of the three packages, you can use the following workaround.

### Workaround Make 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.

### Reporter This vulnerability was responsibly disclosed to the Plone Security Team by Gustav Hansen, F-Secure Consulting. Thank you!

### For more information If 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).