TYPO3 Core

The htmlarea RTE fails to correctly determine the baseURI to define in the editing iframe when a slash is present unencoded in the url parameters.
The case happens with frontend editing. When editing an existing record. An unencoded return url is added to the edit frame parameters. In backend the URL is already properly encoded when present, for example, when searching a record with the global search box and clicking on the record.

Occurs with Mozilla Firefox 51. Does not occur with Google Chrome. Not Verified with Internet Explorer.

1. Set up frontend editing (https://wiki.typo3.org/Frontend_editing and Content Elements (fluid_styled_content) template included for editpanel)
2. Create or choose a Text & Image or Text & Media or any other content with a Rich Text Editor
3. Put a table with default settings in the RTE, it will make the fix visible without inspection
4. Go to the page in frontend and click the edit icon of the created or chosen content
5. In the edit popup, the URL ends with &returnUrl=sysext/backend/Resources/Private/Templates/Close.html
6. In the RTE, table borders are not visible despite activating the show table borders button