Description

The reflected XSS vulnerability occurs to a flaw in the clean_xss_tags() function called in memo.php of Gnuboard 5. This clean_xss_tags() is a Sanitizer that removes XSS-vulnerable tags and attributes. However, it can bypass Sanitizer by using a newline character. (%0A, %0D, ETC)

Proof of Concept

1. Open the https://sir.kr/bbs/memo.php?kind=%0D%3C/noscript%3E%3Csvg/onload=alert(document.domain)%3E&spam=1
2. you can see that occur a xss after login

Impact

Through this vulnerability, an attacker is capable to execute malicious scripts.