PHP Object Injection in Newsletters WordPress Plugin

Executive Summary

CVE-2026-12583 is a vulnerability in the Newsletters WordPress plugin versions before 4.15. It allows unauthenticated attackers to perform PHP Object Injection by exploiting a flaw in how the plugin handles subscriber custom fields.

The vulnerability occurs because the plugin does not prevent deserialization of untrusted input submitted through a public form. Attackers can inject a malicious serialized PHP object into a custom text field via a public subscription form. When this input is later deserialized (e.g., when a newsletter is viewed online), the plugin's bundled gadget chain enables the attacker to write arbitrary files and execute arbitrary code on the server.

• The vulnerability is classified under OWASP A8 (Insecure Deserialization) and CWE-502.
• The CVSS score for this vulnerability is 8.1 (High), indicating a significant risk.

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Detection Guidance

Detecting this vulnerability involves checking for the presence of the vulnerable version of the Newsletters WordPress plugin and monitoring for signs of exploitation.

• Check the installed version of the Newsletters plugin on your WordPress site. If it is version 4.14 or earlier, the site is vulnerable. You can verify the plugin version by navigating to the WordPress admin dashboard, then to 'Plugins', and locating the Newsletters plugin.
• Inspect the WordPress database for suspicious serialized data in custom fields associated with the Newsletters plugin. This may require querying the database directly using SQL commands. For example, you can check the 'wp_postmeta' or 'wp_options' tables for unusual serialized PHP objects.
• Monitor network traffic for unusual submissions to the Newsletters subscription form. Look for POST requests containing serialized PHP objects, which may indicate an attempted exploit.
• Use a web application firewall (WAF) or intrusion detection system (IDS) to detect and block attempts to exploit insecure deserialization vulnerabilities. Configure rules to alert on suspicious serialized input patterns.
• Review server logs for unexpected file creation or modification, particularly in writable directories like '/wp-content/uploads/'. Look for files with unusual names or extensions that may indicate malicious activity.

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Impact Analysis

If you are using an affected version of the Newsletters WordPress plugin (before 4.15), this vulnerability can have severe consequences for your website and server.

• Unauthenticated attackers can execute arbitrary code on your server, potentially gaining full control over it.
• Attackers can write arbitrary files to your server, which may lead to further exploitation, such as installing backdoors or malware.
• The compromise of your server can result in data theft, defacement of your website, or use of your server for malicious activities like phishing or distributing malware.
• Since the attack does not require authentication, any public-facing subscription form on your site could be a potential entry point for attackers.

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Compliance Impact

This vulnerability can have serious implications for compliance with various standards and regulations, depending on the nature of the data your website handles.

• GDPR (General Data Protection Regulation): If your website processes personal data of EU citizens, a breach resulting from this vulnerability could lead to unauthorized access or theft of personal data. Under GDPR, you are required to implement appropriate security measures to protect personal data. Failure to do so (e.g., by not updating the vulnerable plugin) could result in significant fines and legal consequences if a breach occurs.
• HIPAA (Health Insurance Portability and Accountability Act): If your website handles protected health information (PHI) in the U.S., this vulnerability could lead to unauthorized access to PHI. HIPAA requires covered entities to protect PHI from security threats. A breach due to this vulnerability could result in violations, fines, and legal action.
• PCI DSS (Payment Card Industry Data Security Standard): If your website processes payment card information, this vulnerability could lead to unauthorized access to cardholder data. PCI DSS requires strict security controls to protect such data. A breach could result in non-compliance, fines, and loss of ability to process payments.

In general, most data protection regulations require organizations to maintain the confidentiality, integrity, and availability of sensitive data. This vulnerability directly undermines these principles by allowing attackers to execute arbitrary code and access or modify data without authorization. Failing to address such vulnerabilities could be seen as negligence, leading to compliance violations.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Update the Newsletters WordPress plugin to version 4.15 or later. This version contains the fix for the insecure deserialization vulnerability. You can update the plugin through the WordPress admin dashboard under 'Plugins'.
• If updating is not immediately possible, disable the Newsletters plugin to prevent exploitation. This can be done by deactivating the plugin in the WordPress admin dashboard.
• Restrict access to the Newsletters subscription form to trusted users only. This can be done by implementing authentication or CAPTCHA mechanisms to prevent unauthenticated submissions.
• Review and clean up any suspicious data stored in the plugin's custom fields. Remove any serialized PHP objects or unexpected input that may have been injected by an attacker.
• Audit your WordPress installation for signs of compromise, such as unauthorized file modifications, new user accounts, or unexpected code execution. Restore from a known clean backup if necessary.
• Implement a web application firewall (WAF) to block malicious requests targeting this vulnerability. Configure rules to filter out serialized PHP objects in form submissions.

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