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Cross-site Scripting occurrences in Muwire
MuWire is a file publishing and networking tool that protects the identity of its users by using I2P technology. Users of MuWire desktop client prior to version 0.8.8 can be de-anonymized by an attacker who knows their full ID. An attacker could send a message with a subject line containing a URL with an HTML image tag and the MuWire client would try to fetch that image via clearnet, thus exposing the IP address of the user. The problem is fixed in MuWire 0.8.8. As a workaround, users can disable messaging functionality to prevent other users from sending them malicious messages. (2021-07-15, CVE-2021-32750)
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>