Laminas-form Cross-site Scripting

laminas-form is a package for validating and displaying simple and complex forms. When rendering validation error messages via the `formElementErrors()` view helper shipped with laminas-form, many messages will contain the submitted value. However, in laminas-form prior to version 3.1.1, the value was not being escaped for HTML contexts, which could potentially lead to a reflected cross-site scripting attack. Versions 3.1.1 and above contain a patch to mitigate the vulnerability. A workaround is available. One may manually place code at the top of a view script where one calls the `formElementErrors()` view helper. More information about this workaround is available on the GitHub Security Advisory. (2022-01-28, CVE-2022-23598)

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>