CVE-2025-12813 is a critical remote code execution (RCE) vulnerability found in the Holiday class post calendar plugin for WordPress, developed by strix-bubol5. The vulnerability affects all versions up to and including 7.1. It stems from improper control over code generation (CWE-94), specifically due to a lack of sanitization of user-supplied input passed via the 'contents' parameter. When this parameter is used to create a cache file, malicious input can be injected, allowing an attacker to execute arbitrary code on the server hosting the WordPress site. The vulnerability requires no authentication or user interaction, making it highly exploitable remotely over the network. The CVSS v3.1 base score is 9.8, reflecting the critical impact on confidentiality, integrity, and availability. Exploitation could lead to complete server takeover, data exfiltration, defacement, or deployment of further malware. No patches or updates are currently available, and no known exploits have been reported in the wild yet. The vulnerability was publicly disclosed on November 11, 2025, with the CVE reserved a few days earlier. The plugin is widely used in WordPress environments, often on public-facing websites, increasing the attack surface. The lack of input validation and sanitization is a common security flaw that can be mitigated by proper coding practices. Until a patch is released, organizations must rely on defensive measures such as web application firewalls, monitoring, and restricting access to vulnerable components.

For European organizations, this vulnerability poses a severe threat due to the widespread use of WordPress and its plugins across various sectors including e-commerce, media, education, and government websites. Successful exploitation could lead to full server compromise, allowing attackers to steal sensitive data, disrupt services, or use compromised servers as a foothold for lateral movement within networks. The unauthenticated nature of the exploit increases the risk of automated mass scanning and exploitation campaigns targeting vulnerable sites. This could result in reputational damage, regulatory penalties under GDPR due to data breaches, and significant operational downtime. Organizations hosting customer data or critical services on affected WordPress installations are especially at risk. The impact extends beyond the initial compromise, as attackers could deploy ransomware or persistent backdoors. Given the critical CVSS score and ease of exploitation, the threat level for European entities is high, necessitating immediate action to prevent exploitation.

1. Monitor official sources and the plugin vendor for patches or updates and apply them immediately once available. 2. In the absence of a patch, disable or remove the Holiday class post calendar plugin from all WordPress installations to eliminate the attack vector. 3. Deploy and configure web application firewalls (WAFs) with custom rules to detect and block malicious payloads targeting the 'contents' parameter, focusing on suspicious code injection patterns. 4. Conduct thorough input validation and sanitization on all user-supplied data in custom or third-party plugins to prevent similar vulnerabilities. 5. Implement network segmentation to isolate web servers from critical internal systems, limiting lateral movement if compromise occurs. 6. Enable detailed logging and monitor for unusual file creation, modification, or execution activities that could indicate exploitation attempts. 7. Educate website administrators on the risks of using outdated or untrusted plugins and encourage regular security audits. 8. Consider deploying runtime application self-protection (RASP) tools to detect and block exploitation attempts in real time. 9. Review backup and incident response plans to ensure rapid recovery in case of compromise. 10. Restrict administrative access to WordPress dashboards via IP whitelisting or VPN to reduce exposure.