Peter Harteg made an xsrf protection in CMSimple version 3.4 - his last version. It can be selected in the config.php. But this protection did not work as it should. It made several problems when using Oedit. The xsrf protection was included in CMSimple Classic version 3.5 and 3.51 but still causing problems.
Thanks to help and good advices from Christoph this is now fixed in CMSimple Classic version 3.52. The xsrf protection should now works as it should also together with Oedit. The new version can be downloaded from my site: http://cmsimple.p2pnation.eu/
Some reports tells that Oedit doesnt work properly under PHP 5.4. I think the best solution is to use an external editor. Anyway, I think I drop oEdit in the next version of CMSimple Classic.
By the way, I don't really think this xsrf protection is needed. Such an attach is not very likely. But remember that whenever you log into a CMSimple site or any other sites you should log out properly and close the browser before you surf to other sites or click on links in emails etc.