CVE-2025-67911: Newsletters Plugin Object Injection Flaw

CVE-2025-67911 Overview

A critical Deserialization of Untrusted Data vulnerability has been identified in Tribulant Software Newsletters (newsletters-lite) plugin for WordPress. This vulnerability allows attackers to perform PHP Object Injection attacks, potentially leading to remote code execution, unauthorized data access, or complete system compromise on affected WordPress installations.

Critical Impact

Unauthenticated attackers can exploit this PHP Object Injection vulnerability to execute arbitrary code, access sensitive data, or take complete control of vulnerable WordPress sites running Newsletters plugin version 4.11 or earlier.

Affected Products

• Tribulant Software Newsletters (newsletters-lite) plugin versions through 4.11
• WordPress installations using the affected Newsletters plugin
• All WordPress sites with vulnerable plugin versions exposed to network access

Discovery Timeline

• 2026-01-08 - CVE-2025-67911 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-67911

Vulnerability Analysis

This vulnerability stems from improper handling of serialized data within the Newsletters plugin. When the application deserializes user-controlled input without adequate validation, attackers can inject malicious PHP objects that execute arbitrary code during the deserialization process. The vulnerability is classified under CWE-502 (Deserialization of Untrusted Data).

The attack is particularly dangerous because it requires no authentication (PR:N) and no user interaction (UI:N), allowing remote attackers to exploit vulnerable installations directly over the network. Successful exploitation can result in complete compromise of the confidentiality, integrity, and availability of the affected WordPress site.

Root Cause

The root cause of this vulnerability is the use of PHP's unserialize() function on untrusted user input without proper validation or sanitization. When serialized data is passed to this function, PHP reconstructs objects from the serialized string. If an attacker can control the serialized input, they can instantiate arbitrary objects and potentially trigger dangerous "magic methods" such as __wakeup(), __destruct(), or __toString() that may be present in the application's codebase or included libraries.

Attack Vector

The vulnerability is exploitable over the network without requiring authentication. An attacker crafts a malicious serialized PHP payload containing object instances with properties set to trigger dangerous operations when deserialized. The attack flow typically involves:

1. Identifying the vulnerable deserialization endpoint in the Newsletters plugin
2. Analyzing available PHP classes (gadget chains) in the WordPress installation
3. Constructing a serialized payload that chains multiple objects to achieve code execution
4. Sending the malicious payload to the vulnerable endpoint
5. The server deserializes the payload, triggering the exploit chain

The vulnerability allows attackers to leverage Property-Oriented Programming (POP) chains to achieve remote code execution, file manipulation, or database access depending on the available gadget classes in the WordPress environment.

Detection Methods for CVE-2025-67911

Indicators of Compromise

• Unusual serialized data patterns in HTTP request parameters or POST bodies containing O: prefixes indicating PHP object serialization
• Unexpected file creation or modification in WordPress directories, particularly in wp-content/uploads or plugin directories
• Anomalous PHP processes spawning system commands or network connections
• Web server logs showing requests with base64-encoded or URL-encoded serialized object payloads
• Database modifications or unauthorized user account creation

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block serialized PHP object patterns in request data
• Monitor for suspicious unserialize() calls in PHP error logs or application logging
• Deploy file integrity monitoring to detect unauthorized changes to WordPress core files and plugins
• Review web server access logs for unusual POST requests to Newsletters plugin endpoints
• Use WordPress security plugins to scan for signs of compromise

Monitoring Recommendations

• Enable verbose logging for the Newsletters plugin and review logs for deserialization-related errors
• Configure intrusion detection systems to alert on PHP object injection attack signatures
• Monitor outbound network connections from the web server for potential reverse shell callbacks
• Set up alerts for new administrator account creation or privilege escalation events
• Implement real-time file change monitoring on critical WordPress directories

How to Mitigate CVE-2025-67911

Immediate Actions Required

• Update the Newsletters plugin to a patched version immediately once available from Tribulant Software
• If no patch is available, consider temporarily disabling or removing the Newsletters plugin
• Implement WAF rules to block serialized PHP object patterns in incoming requests
• Review WordPress installations for signs of prior compromise
• Restrict network access to WordPress administrative endpoints where possible

Patch Information

The vulnerability affects Newsletters plugin versions through 4.11. Site administrators should check the Patchstack WordPress Plugin Advisory for the latest patch information and update to the newest available version that addresses this vulnerability.

Workarounds

• Disable the Newsletters plugin entirely until a security patch is available
• Implement strict input validation at the web server or WAF level to block serialized PHP objects
• Use PHP configuration to disable dangerous functions that may be leveraged in POP chains (e.g., system(), exec(), passthru())
• Deploy network segmentation to limit the impact of potential compromise
• Consider implementing Content Security Policy headers to mitigate secondary attack vectors

# Example: Block serialized PHP objects in Apache .htaccess
# Add to WordPress root .htaccess file
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{QUERY_STRING} (^|&).*O:[0-9]+: [NC,OR]
RewriteCond %{REQUEST_BODY} .*O:[0-9]+:
RewriteRule .* - [F,L]
</IfModule>