CVE-2026-3018: Newsletters Plugin SQL Injection Vulnerability

Technical summary

This vulnerability is a classic SQL injection (CWE-89) stemming from insufficient input validation and lack of parameterized query preparation. The 'wpmlsubscriber_id' parameter is concatenated directly into SQL queries without proper escaping or prepared statement use. An attacker can inject time-based SQL payloads to infer database structure and content character-by-character through response time analysis. The unauthenticated nature of the attack vector significantly increases exploitability since no account access is required.

Business impact

Successful exploitation enables unauthorized extraction of sensitive data from the WordPress database, potentially including user credentials, subscriber information, email addresses, and other personally identifiable information (PII). For organizations relying on the Newsletters plugin for subscriber management, this represents a direct data breach risk with potential regulatory consequences under GDPR, CCPA, and similar privacy laws. Additionally, attackers may use extracted information for further social engineering or credential-based attacks.

Affected systems

The Newsletters plugin for WordPress in all versions up to and including 4.13 is vulnerable. Any WordPress installation using this plugin is at risk, regardless of additional security plugins or WAF rules, since the vulnerability exists at the application logic level. Self-hosted WordPress sites and managed WordPress hosting platforms are equally affected if the vulnerable plugin version is active.

Exploitability

The CVSS 3.1 score of 7.5 (HIGH) reflects the high exploitability of this flaw. Exploitation requires only network access and no authentication, making it trivial for unauthenticated attackers to craft malicious requests. Time-based SQL injection techniques are well-documented and tooling is publicly available. While response-time-based data exfiltration is slower than error-based injection, it is reliable and difficult to detect with basic monitoring. The lack of CISA KEV listing does not diminish the practical exploitability—it indicates active exploitation is not yet widespread in the wild, but the technical barrier to exploitation is low.

Remediation

Update the Newsletters plugin to a patched version released after 4.13. Verify the specific patched version number against the official WordPress plugin repository and the vendor's security advisory. In the interim, if an update is unavailable or delayed, consider disabling the plugin or restricting access to the affected endpoint via web application firewall rules targeting the 'wpmlsubscriber_id' parameter.

Patch guidance

Monitor the official WordPress Newsletters plugin repository for security updates. When a patched version is released, apply it immediately to all WordPress installations using this plugin. Test the update in a staging environment first to ensure compatibility with other active plugins and your site configuration. Because the vulnerability is unauthenticated and high-severity, prioritize this patching task above routine maintenance updates.

Detection guidance

Look for HTTP requests containing SQL injection syntax in the 'wpmlsubscriber_id' parameter, such as time-delay payloads (SLEEP, BENCHMARK, WAITFOR) or boolean-based logic (AND 1=1, OR 1=1). Monitor database query logs for unusual query patterns originating from the Newsletters plugin. Implement WAF rules to block requests with SQL keywords in this parameter. Enable WordPress logging and audit the database access logs for unexpected SELECT statements targeting sensitive tables like wp_users and wp_usermeta.

Why prioritize this

This vulnerability merits immediate attention because it combines high CVSS severity (7.5) with full unauthenticated exploitability and confidentiality impact on sensitive subscriber and user data. The lack of authentication requirement means any internet-facing WordPress site using the vulnerable plugin version is at active risk. Time-based SQL injection, while slower than error-based variants, remains reliably exploitable and difficult to prevent without patching. Organizations must prioritize patching this vulnerability before they become part of broader reconnaissance or data harvesting campaigns.

Risk score, explained

The CVSS 3.1 score of 7.5 reflects a HIGH severity due to the combination of: (1) network-based attack vector requiring no privileged access, (2) no user interaction required, (3) no scope change, and (4) high confidentiality impact. The lack of integrity or availability impact prevents a higher score, but the confidentiality risk alone—extraction of subscriber lists, PII, and potentially password hashes—justifies immediate remediation.

Frequently asked questions