CVE-2026-3253 in Signup Forms Plugin
Summary
by MITRE • 09/24/2026
The MailerLite – Signup forms (official) plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the forms() method of the AdminController class in all versions up to, and including, 1.7.21. This makes it possible for authenticated attackers, with Contributor-level access and above, to create or delete arbitrary signup forms.
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Analysis
by VulDB Data Team • 09/24/2026
The MailerLite Signup Forms plugin for WordPress contains a critical authorization flaw within its administrative interface that allows users with relatively low privilege levels to perform actions intended only for higher-privileged administrators. Specifically, the vulnerability resides in the forms method of the AdminController class, which handles the creation and deletion of signup forms used by website owners to collect subscriber information. In versions up to 1.7.21, this endpoint fails to verify whether the requesting user possesses the necessary capabilities or permissions before executing data modification operations. This absence of a proper capability check represents a fundamental breakdown in access control logic, where the application assumes that any authenticated request is valid without validating the scope of authority granted to the specific user account initiating it.
From a technical perspective, this issue classifies as an Insecure Direct Object Reference or more accurately a Broken Access Control vulnerability, aligning with CWE-269 which covers Improper Privilege Management. The flaw exploits the trust relationship between WordPress core and its plugin ecosystem by bypassing standard role-based access controls. An attacker who has obtained Contributor-level credentials or higher can interact directly with the administrative endpoints associated with form management. Because the server does not enforce a secondary authorization check on these specific actions, it processes requests to create new forms or delete existing ones regardless of whether the user is authorized for such tasks. This allows for arbitrary data manipulation within the context of the compromised website's MailerLite integration.
The operational impact of this vulnerability extends beyond simple administrative nuisance. An attacker with Contributor access can inject malicious signup forms designed to harvest sensitive personal information from legitimate visitors, thereby facilitating phishing campaigns or identity theft. Alternatively, an attacker could delete existing forms, causing a disruption in business operations and leading to loss of potential leads or customer data. In the context of supply chain attacks, compromising this plugin allows threat actors to pivot into other areas of the WordPress environment if they can leverage the stolen credentials for further exploitation. The ability to modify these forms effectively grants the attacker control over how user data is collected and processed by the MailerLite service, potentially violating privacy regulations such as GDPR or CCPA depending on the jurisdiction and nature of the data involved.
This vulnerability maps directly to MITRE ATT&CK techniques related to Privilege Escalation and Collection. Specifically, it aligns with T1078 Valid Accounts, where attackers use legitimate credentials that have been compromised or misconfigured to gain access. The action of creating malicious forms falls under T1563 Remote Service Tool Installation if the form is used to install further malware, while data harvesting relates to T1114 Email Collection and T1539 Steal Web Session Cookie if session tokens are targeted through injected scripts within the form fields. Understanding these mappings helps security teams identify similar patterns in other plugins that may lack robust input validation and authorization checks on administrative endpoints.
To mitigate this risk, site administrators should immediately update the MailerLite Signup Forms plugin to version 1.7.22 or later, where the missing capability check has been addressed by implementing proper WordPress role verification functions such as current_user_can before processing form creation or deletion requests. Until an update is applied, it is advisable to restrict access to the administrative dashboard using IP whitelisting if possible and ensure that all user accounts adhere strictly to the principle of least privilege. Regularly auditing plugin code for missing authorization checks on sensitive endpoints can prevent similar vulnerabilities in other installed extensions. Additionally, enabling two-factor authentication for all administrator and editor-level accounts adds a layer of defense against credential theft, reducing the likelihood of an attacker gaining the initial Contributor access required to exploit this flaw.