Description

When uploading a new module, the description of the module can contain JavaScript code. After uploading the new module and looking at the Details page, the JavaScript code would be executed.

Proof of Concept

• I downloaded this module

https://github.com/friends-of-forkcms/fork-cms-module-banners/archive/master.zip

, unzipped it and adjusted the description path of the file

src/Backend/Modules/Banners/info.xml

to this

<description>
    <![CDATA[
        The banners module.
        <script>alert(4);</script>
    ]]>
</description>

After adjusting the info.xml file, pack all files back to a zip file and upload it as new module.
After upload, visit the Details page of this module.

Impact

Executing any JavaScript an attacker could think of. By default, it is used to steal session cookies.