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Cross-site Scripting occurrences in Wp Svg Images
The WP SVG images WordPress plugin before 3.4 did not sanitise the SVG files uploaded, which could allow low privilege users such as author+ to upload a malicious SVG and then perform XSS attacks by inducing another user to access the file directly. In v3.4, the plugin restricted such upload to editors and admin, with an option to also allow author to do so. The description of the plugin has also been updated with a security warning as upload of such content is intended. (2021-07-06, CVE-2021-24386)
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>