CVE-2025-12813: WordPress Holiday Class Plugin RCE Flaw

CVE-2025-12813 Overview

The Holiday Class Post Calendar plugin for WordPress contains a critical Remote Code Execution (RCE) vulnerability affecting all versions up to and including 7.1. The flaw exists in the contents parameter due to insufficient sanitization of user-supplied data during cache file creation. This vulnerability allows unauthenticated attackers to execute arbitrary code on the server, potentially leading to complete site compromise.

Critical Impact

Unauthenticated attackers can achieve full remote code execution on WordPress sites running vulnerable versions of the Holiday Class Post Calendar plugin, enabling complete server takeover without requiring any authentication or user interaction.

Affected Products

• Holiday Class Post Calendar plugin for WordPress versions ≤ 7.1
• WordPress sites utilizing the vulnerable plugin versions
• Web servers hosting affected WordPress installations

Discovery Timeline

• 2025-11-11 - CVE-2025-12813 published to NVD
• 2025-11-12 - Last updated in NVD database

Technical Details for CVE-2025-12813

Vulnerability Analysis

This vulnerability falls under CWE-94 (Improper Control of Generation of Code), commonly referred to as Code Injection. The flaw stems from the plugin's failure to properly sanitize user-controlled input before incorporating it into dynamically generated cache files. When an attacker submits malicious content through the contents parameter, the unsanitized data is written directly to a cache file that the server subsequently processes and executes.

The unauthenticated nature of this vulnerability significantly amplifies its risk profile. Attackers require no prior access, credentials, or user interaction to exploit the flaw. The attack can be executed remotely over the network, making internet-facing WordPress installations particularly vulnerable to automated scanning and exploitation attempts.

Root Cause

The root cause of this vulnerability lies in the absence of input validation and sanitization routines when processing user-supplied data destined for cache file creation. The plugin directly writes the contents of the contents parameter to a PHP cache file without filtering potentially malicious code constructs. This architectural oversight allows attackers to inject arbitrary PHP code that executes within the context of the web server when the cache file is processed.

Attack Vector

The attack leverages the network-accessible nature of WordPress plugins. An attacker sends a crafted HTTP request containing malicious PHP code within the contents parameter. The vulnerable plugin writes this payload to a server-side cache file. Upon cache file execution or inclusion, the injected code runs with the privileges of the web server process, granting the attacker code execution capabilities on the target system.

The vulnerability mechanism exploits the cache file generation process in the plugin. An attacker crafts a malicious request to the plugin endpoint containing PHP code within the contents parameter. When the plugin creates the cache file, the malicious payload is written without sanitization. Subsequent access to this cache file results in arbitrary code execution. For additional technical details, refer to the WordPress Plugin Code Reference and the Wordfence Vulnerability Report.

Detection Methods for CVE-2025-12813

Indicators of Compromise

• Unexpected PHP files or modified cache files within the plugin directory wp-content/plugins/holiday-class-post-calendar/
• Web server access logs showing unusual POST requests to plugin endpoints containing encoded PHP code or shell commands
• Presence of webshells, backdoors, or unfamiliar PHP files in WordPress directories
• Anomalous outbound network connections originating from the web server process

Detection Strategies

• Monitor web application firewall (WAF) logs for requests containing PHP code patterns targeting the plugin's endpoints
• Implement file integrity monitoring on the WordPress installation, particularly the plugin cache directories
• Deploy endpoint detection and response (EDR) solutions to identify unauthorized process execution by the web server
• Analyze server logs for requests with suspicious contents parameter values containing base64-encoded data or PHP tags

Monitoring Recommendations

• Enable detailed logging for WordPress plugin activity and cache file operations
• Configure real-time alerting for any file creation or modification within the plugin's directory structure
• Implement behavioral analysis to detect anomalous code execution patterns from web server processes
• Monitor for privilege escalation attempts or lateral movement following potential exploitation

How to Mitigate CVE-2025-12813

Immediate Actions Required

• Immediately disable or remove the Holiday Class Post Calendar plugin from all WordPress installations
• Audit the affected plugin directory for any unexpected or recently modified PHP files
• Review web server access logs for evidence of exploitation attempts
• Consider implementing Web Application Firewall (WAF) rules to block requests containing PHP code in parameters

Patch Information

Check the official WordPress plugin repository for an updated version of the Holiday Class Post Calendar plugin that addresses this vulnerability. The Wordfence Vulnerability Report provides additional details on affected versions and remediation guidance. If no patched version is available, consider using an alternative calendar plugin until a security update is released.

Workarounds

• Remove the Holiday Class Post Calendar plugin entirely until a patched version is available
• If removal is not immediately possible, restrict access to the plugin's endpoints via .htaccess or web server configuration
• Implement strict input validation at the web server or WAF level to block requests containing PHP code constructs
• Consider placing the WordPress installation behind an application-aware reverse proxy with request filtering capabilities

# Example: Block access to the vulnerable plugin via Apache .htaccess
# Place this in wp-content/plugins/holiday-class-post-calendar/.htaccess
<Files "*.php">
    Order Deny,Allow
    Deny from all
    # Allow only WordPress internal requests if absolutely necessary
    # Allow from 127.0.0.1
</Files>