Proton Cross-site Scripting

Proton v0.2.0 allows an attacker to create a malicious link inside a markdown file. When the victim clicks the link, the application opens the site in the current frame allowing an attacker to host JavaScript code in the malicious link in order to trigger an XSS attack. The 'nodeIntegration' configuration is set to on which allows the 'webpage' to use 'NodeJs' features, an attacker can leverage this to run OS commands. (2022-05-20, CVE-2022-25224)

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>