The Kirki WordPress plugin before 6.0.12 does not sanitise or escape the email subject and body values supplied in a request before including them in the password-reset email it sends as HTML, allowing unauthenticated users to inject arbitrary HTML into the message delivered to a registered user, which can be used for phishing.
The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.