A serious bug found as CVE-2021-39341 in the OptinMonster plugin allows unauthorized API access and disclosure of sensitive information on about one million WordPress pages.
The OptinMonster (a popular WordPress plugin used to create beautiful opt-in forms that help website owners convert visitors to subscribers/customers) flaw was discovered by Chloe Chamberland.
They claim that while OptinMonster’s power relies on API endpoints that provides space for seamless integration and a streamlined design process, the implementation of these endpoints is not always safe, as one of the endpoints (/wp-json/omapp/v1/support) could disclose data such as the full path of the site on the server, API keys for requests on the sites, and more.
With the API in the hands of an attacker, he could make changes to the OptinMonster accounts or create malicious JavaScript snippets on the website.