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Cross-site Scripting occurrences in Timetracker
anuko/timetracker is an, open source time tracking system. In affected versions Time Tracker uses browser_today hidden control on a few pages to collect the today's date from user browsers. Because of not checking this parameter for sanity in versions prior to 1.19.30.5601, it was possible to craft an html form with malicious JavaScript, use social engineering to convince logged on users to execute a POST from such form, and have the attacker-supplied JavaScript to be executed in user's browser. This has been patched in version 1.19.30.5600. Upgrade is recommended. If it is not practical, introduce ttValidDbDateFormatDate function as in the latest version and add a call to it within the access checks block. (2021-10-18, CVE-2021-41156)
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>