CVE-2023-5098 is a high-severity vulnerability affecting the WordPress plugin "Campaign Monitor Forms by Optin Cat" in versions prior to 2.5.6. The core issue is an improper access control weakness (CWE-284) that allows users with low privileges, such as subscribers, to overwrite arbitrary site options by setting them to the string "true". This vulnerability arises because the plugin fails to properly restrict access to sensitive option modification functions, allowing unauthorized users to escalate their impact on the site configuration. The exploitation does not require user interaction beyond having a low-privilege account and can be performed remotely over the network (AV:N). The attack complexity is low (AC:L), and no UI interaction is needed (UI:N). The scope remains unchanged (S:U), meaning the vulnerability affects only the privileges of the compromised component without extending to other components. Although confidentiality is not impacted (C:N), the integrity and availability of the site are severely affected (I:H, A:H), as attackers can manipulate site options to disrupt normal operations, potentially causing denial of service or other harmful outcomes. No known exploits are currently reported in the wild, but the high CVSS score of 8.1 indicates a significant risk if exploited. The vulnerability was publicly disclosed on October 31, 2023, and is tracked by WPScan and CISA, highlighting its relevance to WordPress site security. The lack of available patches at the time of disclosure emphasizes the need for immediate mitigation efforts by site administrators using this plugin.

For European organizations, this vulnerability poses a substantial risk, especially for those relying on WordPress sites with the Campaign Monitor Forms by Optin Cat plugin for marketing, customer engagement, or data collection. Successful exploitation could lead to site misconfiguration, service disruption, or denial of service, impacting business continuity and user trust. Organizations in sectors such as e-commerce, media, and public services that utilize WordPress extensively may face operational downtime and reputational damage. Since the attack requires only low-privilege user accounts, any compromised or malicious subscriber account could be leveraged to disrupt site functionality. This risk is heightened in environments with weak user account management or where subscriber roles are widely granted. Additionally, the integrity of site configurations is critical for compliance with European data protection regulations (e.g., GDPR), and unauthorized changes could lead to regulatory scrutiny if personal data handling is affected. The vulnerability's network-exploitable nature means remote attackers can attempt exploitation without physical access, increasing the attack surface for European organizations with public-facing WordPress sites.

1. Immediate upgrade: Site administrators should update the Campaign Monitor Forms by Optin Cat plugin to version 2.5.6 or later once available, as this will contain the official patch addressing the improper access control issue. 2. Privilege review: Audit and minimize the number of users assigned low-privilege roles such as subscribers, ensuring only trusted individuals have such access. 3. Temporary access restrictions: Until a patch is applied, implement web application firewall (WAF) rules to monitor and block suspicious requests attempting to modify site options via the plugin endpoints. 4. Monitor logs: Enable detailed logging of option changes and user activities related to the plugin to detect unauthorized modifications early. 5. Harden WordPress security: Disable or restrict plugin and theme editing capabilities for low-privilege users, and consider using security plugins that enforce stricter access controls. 6. Isolate critical sites: For high-value or sensitive WordPress installations, consider isolating the site or restricting access to subscriber functionalities to reduce attack vectors. 7. Incident response readiness: Prepare to quickly restore site configurations from backups if unauthorized changes are detected, minimizing downtime.