Flatcore Cross-site Scripting

An issue was discovered in flatCore before 2.0.0 build 139. A reflected XSS vulnerability was identified in the media_filter HTTP request body parameter for the acp interface. The affected parameter accepts malicious client-side script without proper input sanitization. For example, a malicious user can leverage this vulnerability to steal cookies from a victim user and perform a session-hijacking attack, which may then lead to unauthorized access to the site. (2021-01-15, CVE-2021-23838)

An issue was discovered in flatCore before 2.0.0 build 139. A stored XSS vulnerability was identified in the prefs_smtp_psw HTTP request body parameter for the acp interface. An admin user can inject malicious client-side script into the affected parameter without any form of input sanitization. The injected payload will be executed in the browser of a user whenever one visits the affected module page. (2021-01-15, CVE-2021-23836)

flatCore before 1.5.7 allows XSS by an admin via the acp/acp.php?tn=pages&sub=edit&editpage=1 page_linkname, page_title, page_content, or page_extracontent parameter, or the acp/acp.php?tn=system&sub=sys_pref prefs_pagename, prefs_pagetitle, or prefs_pagesubtitle parameter. (2020-08-09, CVE-2020-17451)

Cross site scripting is an attack where a web page executes code that is injected by an adversary. It usually appears, when users input is presented. This attack can be used to impersonate a user, take over control of the session, or even steal API keys.

The attack can be executed e.g. when you application injects the request parameter directly into the HTML code of the page returned to the user:

https://server.com/confirmation?message=Transaction+Complete

what results in:

<span>Confirmation: Transaction Complete</span>

In that case the message can be modified to become a valid Javascript code, e.g.:

https://server.com/confirmation?message=<script>dangerous javascript code here</script>

and it will be executed locally by the user's browser with full access to the user's personal application/browser data:

<span>Confirmation: <script>dangerous javascript code here</script></span>