CVE-2023-3407 in Subscribe2 Plugin
Summary
by MITRE • 06/28/2023
The Subscribe2 plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 10.40. This is due to missing or incorrect nonce validation when sending test emails. This makes it possible for unauthenticated attackers to send test emails with custom content to users on sites running a vulnerable version of this plugin via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.
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Analysis
by VulDB Data Team • 04/10/2026
The Subscribe2 plugin for WordPress represents a widely used subscription management tool that allows website administrators to manage email subscriptions for their users. This plugin enables users to subscribe to newsletters and receive updates from websites, making it an integral part of many WordPress installations. However, version 10.40 and earlier contained a critical security flaw that exposed websites to cross-site request forgery attacks, potentially compromising user data and website integrity. The vulnerability stems from insufficient validation mechanisms within the plugin's email sending functionality, creating an exploitable gap in the security architecture.
The technical flaw manifests in the plugin's handling of nonce validation during test email sending operations. A nonce is a cryptographic value that is unique to each request and is designed to prevent CSRF attacks by ensuring that requests originate from legitimate sources. In vulnerable versions of Subscribe2, the plugin failed to properly validate these nonces when processing test email requests, allowing attackers to forge requests that appeared to come from legitimate administrators. This weakness specifically affects the test email functionality, which should require proper authentication and validation before executing email operations, but instead accepts requests without adequate verification of the requester's identity.
The operational impact of this vulnerability extends beyond simple email delivery manipulation, creating a potential attack vector for more sophisticated social engineering campaigns. An attacker can craft malicious links that, when clicked by an authenticated administrator, trigger unauthorized test email sending operations. These forged requests can include custom email content that may contain phishing attempts, malicious links, or other payloads designed to exploit the administrator's trust in the website's functionality. The vulnerability particularly affects sites where administrators frequently click on links from external sources or where the attack vector involves legitimate-looking administrative tasks that could be easily deceived.
This vulnerability aligns with CWE-352, which specifically addresses Cross-Site Request Forgery vulnerabilities in software applications. The flaw demonstrates a classic example of insufficient request validation where the application fails to verify the authenticity of incoming requests, making it susceptible to exploitation by attackers who can manipulate the request parameters. From an ATT&CK framework perspective, this vulnerability maps to techniques involving social engineering and privilege escalation, as attackers can leverage the administrator's trust to execute unauthorized actions. The attack requires minimal technical expertise but can yield significant impact, particularly when combined with other social engineering techniques that might trick administrators into clicking malicious links.
The recommended mitigation strategy involves immediate upgrading to the patched version of the Subscribe2 plugin, which addresses the nonce validation issue by implementing proper cryptographic verification mechanisms for all email sending operations. Administrators should also implement additional security measures such as restricting access to administrative functions through IP whitelisting, implementing multi-factor authentication for administrative accounts, and conducting regular security audits of installed plugins. Organizations should consider implementing web application firewalls that can detect and block suspicious CSRF attack patterns, as well as educating administrators about the risks of clicking unverified links and the importance of verifying the authenticity of requests before performing administrative actions. Regular monitoring of plugin security advisories and maintaining up-to-date security practices are essential for preventing similar vulnerabilities from affecting the WordPress ecosystem.