Simplesamlphp Cross-site Scripting

Cross-site scripting in SimpleSAMLphp before version 1.18.4. The www/erroreport.php script allows error reports to be submitted and sent to the system administrator. Starting with SimpleSAMLphp 1.18.0, a new SimpleSAML\Utils\EMail class was introduced to handle sending emails, implemented as a wrapper of an external dependency. This new wrapper allows us to use Twig templates in order to create the email sent with an error report. Since Twig provides automatic escaping of variables, manual escaping of the free-text field in www/errorreport.php was removed to avoid double escaping. However, for those not using the new user interface yet, an email template is hardcoded into the class itself in plain PHP. Since no escaping is provided in this template, it is then possible to inject HTML inside the template by manually crafting the contents of the free-text field. (2020-01-24, CVE-2020-5226)

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>