W4 Post List < 2.4.6 - Contributor+ Stored XSS

The plugin does not validate and escape some of its block options before outputting them back in a page/post where the block is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.

PoC

On a post, add a “W4 Post List” block, select a list and put the following payload in the “Additional CSS class(es)” option: " onmouseover=“alert(/XSS/)” style=“background:red;” The XSS will be triggered when previewing/viewing the post and moving the mouse over the red block