Overview
This article details a critical security vulnerability, CVE-2025-66055, affecting the Email Subscribers & Newsletters plugin for WordPress. This vulnerability, a Deserialization of Untrusted Data issue, allows for Object Injection and impacts versions up to and including 5.9.10. It is crucial for website administrators using this plugin to understand the risks and take immediate action to mitigate them.
Technical Details
The vulnerability stems from the insecure handling of deserialized data. The Email Subscribers & Newsletters plugin, in versions 5.9.10 and earlier, fails to properly sanitize data before deserialization. An attacker could potentially inject malicious PHP objects into the application’s memory by exploiting this flaw. This can lead to arbitrary code execution on the server. The specific vulnerable code area isn’t detailed publicly (at the time of this writing based on the reference provided), but the core problem lies within deserialization processes where user-supplied data influences the objects being created and manipulated.
CVSS Analysis
According to available information, a CVSS score hasn’t been assigned at this time. However, the nature of Object Injection vulnerabilities is inherently severe. Even without an official CVSS score, the ability to execute arbitrary code should be considered a high-risk security issue. We strongly recommend immediate patching.
Possible Impact
Successful exploitation of this vulnerability could have severe consequences, including:
- Arbitrary Code Execution: An attacker could execute arbitrary code on the web server, potentially leading to complete system compromise.
- Data Breach: Sensitive data stored on the server could be accessed and stolen.
- Website Defacement: The attacker could modify the website’s content, causing reputational damage.
- Malware Distribution: The compromised website could be used to distribute malware to visitors.
- Backdoor Creation: An attacker could create a backdoor for persistent access, enabling them to re-compromise the system at any time.
The impact of this vulnerability is significant, requiring immediate attention and remediation.
Mitigation and Patch Steps
- Update the Plugin: The primary mitigation step is to immediately update the Email Subscribers & Newsletters plugin to the latest available version. Check the WordPress plugin repository for updates. A patched version addressing this vulnerability should be available.
- Check for Compromise: After updating, thoroughly examine your website and server logs for any suspicious activity that may indicate prior exploitation. Look for unexpected file modifications, new user accounts, or unusual network traffic.
- Web Application Firewall (WAF): Implement a Web Application Firewall (WAF) with rules to detect and block deserialization attacks. This provides an additional layer of protection.
- Code Review (If Possible): For advanced users, consider conducting a code review of the plugin to identify and address any other potential vulnerabilities.
- Principle of Least Privilege: Ensure that your WordPress user accounts and server accounts have only the necessary permissions. This limits the damage an attacker can cause if they gain access.
References
Patchstack Vulnerability Database: Email Subscribers & Newsletters Plugin 5.9.10 – PHP Object Injection Vulnerability
CVE-2025-66055 at MITRE
