[Bug reporting] XSS vulnerabilty in wp_kses_bad_protocol in wp-includes/kses.php (CVE-2019-20041)

[seongil-wi]

Hi

I found a known XSS vulnerability in the recent version of Phinch.
In particular, the bug we report is a known bug by CVE-2019-20041.

wp_kses_bad_protocol in wp-includes/kses.php in WordPress before 5.3.1 mishandles the HTML5 colon named entity, allowing attackers to bypass input sanitization, as demonstrated by the javascript: substring.

Please check this line:

Phinch/blog/wp-includes/kses.php

Line 1057 in c87966e

$string2 = preg_split( '/:|&#0*58;|&#x0*3a;/i', $string, 2 );

Thanks!