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Cross-site Scripting occurrences in Cost Calculator

The Cost Calculator WordPress plugin before 1.6 allows users with a role as low as Contributor to perform Stored Cross-Site Scripting attacks via the Description fields of a Cost Calculator > Price Settings (which gets injected on the edit page as well as any page that embeds the calculator using the shortcode), as well as the Text Preview field of a Project (injected on the edit project page) (2022-03-07, CVE-2021-24821)

Why Cross-site Scripting can be dangerous

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>

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