CVE-2025-4803 is a high-severity vulnerability affecting the WordPress plugin 'Glossary by WPPedia – Best Glossary plugin for WordPress' developed by steinrein. The vulnerability arises from unsafe deserialization of untrusted data (CWE-502) in the 'posttypes' parameter, which allows PHP Object Injection (POI). This vulnerability exists in all versions up to and including 1.3.0 of the plugin. Exploitation requires an attacker to have authenticated Administrator-level access or higher on the WordPress site. Without such privileges, exploitation is not possible. The vulnerability itself does not contain a known gadget or POP (Property Oriented Programming) chain within the plugin code, meaning that on its own, it does not lead to direct code execution or other impacts. However, if the target WordPress installation has other plugins or themes installed that contain POP chains, an attacker could leverage this vulnerability to perform malicious actions such as arbitrary file deletion, sensitive data disclosure, or remote code execution depending on the capabilities of the POP chain present. The CVSS v3.1 base score is 7.2, reflecting high severity due to the potential for confidentiality, integrity, and availability impacts, combined with network attack vector, low attack complexity, and the requirement for high privileges but no user interaction. No known exploits are currently in the wild, and no patches have been linked yet. This vulnerability highlights the risks of unsafe deserialization in PHP applications, especially in complex plugin ecosystems like WordPress where chained vulnerabilities can escalate impact.

For European organizations running WordPress sites with the affected Glossary by WPPedia plugin, this vulnerability poses a significant risk if the attacker can gain Administrator-level access. Given that WordPress is widely used across Europe for business, government, and public sector websites, the potential impact includes unauthorized data access, website defacement, data loss, or full site compromise if combined with other vulnerable plugins or themes. The requirement for admin privileges limits the attack surface primarily to insiders or attackers who have already compromised lower-level accounts or exploited other vulnerabilities to escalate privileges. However, once exploited, the attacker could disrupt business operations, leak sensitive information, or use the compromised site as a pivot point for further attacks. This is particularly critical for organizations handling personal data under GDPR, as breaches could lead to regulatory penalties and reputational damage. The lack of a direct POP chain in the plugin means the impact depends heavily on the presence of other vulnerable components, which is common in complex WordPress environments. Therefore, European organizations with extensive plugin usage and less stringent access controls are at higher risk.

1. Immediately restrict Administrator-level access to trusted personnel only and enforce strong authentication mechanisms such as multi-factor authentication (MFA) to reduce the risk of privilege escalation. 2. Audit installed plugins and themes to identify and update or remove those known to contain POP chains or unsafe deserialization patterns. 3. Monitor WordPress sites for unusual administrator activity and signs of exploitation attempts, including file changes and unexpected requests to the 'posttypes' parameter. 4. Apply principle of least privilege by limiting plugin and theme installations to only those necessary and vetted for security. 5. Implement web application firewalls (WAF) with rules to detect and block suspicious deserialization payloads or PHP object injection attempts targeting the affected parameter. 6. Regularly update the Glossary by WPPedia plugin once a patch is released by the vendor. 7. Conduct security reviews and penetration testing focused on chained vulnerabilities in the WordPress environment to identify potential POP chains that could be exploited in combination with this vulnerability. 8. Backup WordPress sites and databases regularly to enable recovery in case of compromise.