Fediverse Embeds embeds fediverse posts on WordPress sites. Prior to version 1.5.9, Fediverse Embeds registered the unauthenticated AJAX action wp_ajax_nopriv_ftf_get_site_info (includes/Site_Info.php) that verified a nonce ftf-fediverse-embeds-nonce and then called file_get_html($site_url) on the attacker-supplied URL. The same nonce was enqueued onto every public page containing a fediverse embed (via includes/Enqueue_Assets.php lines 41-46 + includes/Helpers.php lines 64-83), so the nonce gate was not an authentication boundary; any visitor of a public post with an embed could grab it and reuse it. This issue has been patched in version 1.5.9.
Analyzing vulnerability vectors…