CVE-2025-13866 is a vulnerability identified in the Flow-Flow Social Feed Stream plugin for WordPress, specifically in versions 3.0.0 through 4.7.5. The root cause is a missing authorization check (CWE-862) on the AJAX action 'flow_flow_social_auth', which is responsible for handling certain plugin settings modifications. This flaw allows any authenticated user with at least Subscriber-level privileges to bypass intended access controls and modify plugin settings arbitrarily. The attacker can inject arbitrary JavaScript code into the plugin's settings page, which executes whenever an administrator or user with access views that page. This creates a vector for persistent cross-site scripting (XSS) attacks, potentially enabling session hijacking, credential theft, or further exploitation within the WordPress environment. The vulnerability is remotely exploitable over the network without requiring user interaction beyond authentication. The CVSS 3.1 base score is 6.4 (medium), reflecting network attack vector, low attack complexity, low privileges required, no user interaction, and partial confidentiality and integrity impacts but no availability impact. No known exploits are currently reported in the wild, and no official patches have been linked yet. However, the vulnerability poses a significant risk to WordPress sites using this plugin, especially those with multiple users having Subscriber or higher roles.

For European organizations, this vulnerability can lead to unauthorized modification of plugin settings and injection of malicious JavaScript, which may compromise site integrity and confidentiality. Attackers could leverage this to conduct persistent XSS attacks, potentially stealing session cookies or credentials of higher-privileged users, leading to further compromise of the WordPress environment. This is particularly concerning for organizations relying on WordPress for public-facing websites or internal portals where multiple users have authenticated access. The impact is limited to confidentiality and integrity, with no direct availability impact. However, the injected scripts could be used to pivot attacks or spread malware, increasing overall risk. Organizations in sectors such as government, finance, and media, which often use WordPress and have strict data protection requirements under GDPR, may face regulatory and reputational damage if exploited.

1. Immediately restrict access to the Flow-Flow Social Feed Stream plugin settings page to only trusted administrators by adjusting WordPress user roles and capabilities. 2. Monitor existing user accounts and remove or downgrade unnecessary Subscriber or higher-level accounts to minimize the attack surface. 3. Implement Web Application Firewall (WAF) rules to detect and block suspicious AJAX requests targeting 'flow_flow_social_auth'. 4. Regularly audit plugin settings pages for unauthorized JavaScript injections or unexpected changes. 5. Apply security headers such as Content Security Policy (CSP) to limit the impact of injected scripts. 6. Once available, promptly update the plugin to a patched version that includes proper authorization checks. 7. Educate site administrators about the risks of granting excessive privileges to low-level users. 8. Consider isolating WordPress administrative interfaces behind VPNs or IP whitelisting to reduce exposure.