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Cross-site Scripting occurrences in Easy Forms For Mailchimp
A vulnerability classified as problematic has been found in yikes-inc-easy-mailchimp-extender Plugin up to 6.8.5. This affects an unknown part of the file admin/partials/ajax/add_field_to_form.php. The manipulation of the argument field_name/merge_tag/field_type/list_id leads to cross site scripting. It is possible to initiate the attack remotely. Upgrading to version 6.8.6 is able to address this issue. The name of the patch is 3662c6593aa1bb4286781214891d26de2e947695. It is recommended to upgrade the affected component. The associated identifier of this vulnerability is VDB-215307. (2022-12-12, CVE-2021-4244)
The Easy Forms for Mailchimp WordPress plugin before 6.8.6 does not sanitise and escape the field_name and field_type parameters before outputting them back in attributes, leading to Reflected Cross-Site Scripting issues (2022-01-24, CVE-2021-24985)
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>