CVE-2025-49855 is a Cross-site Scripting (XSS) vulnerability classified under CWE-79, specifically a DOM-based XSS issue found in the Meks Flexible Shortcodes plugin, versions up to and including 1.3.7. This vulnerability arises due to improper neutralization of input during web page generation, allowing malicious scripts to be injected and executed within the context of a user's browser. The flaw is exploitable remotely (AV:N) with low attack complexity (AC:L), but requires the attacker to have some level of privileges (PR:L) and user interaction (UI:R), such as tricking a user into clicking a crafted link. The vulnerability affects the confidentiality, integrity, and availability of affected web applications, as it can lead to session hijacking, defacement, or redirection to malicious sites. The scope is changed (S:C), indicating that the vulnerability can affect resources beyond the vulnerable component itself. The CVSS v3.1 base score is 6.5, categorized as medium severity. No known exploits are currently reported in the wild, and no official patches have been published at the time of analysis. The vulnerability is specific to the Meks Flexible Shortcodes plugin, which is commonly used in WordPress environments to add shortcode functionality for content management. The issue is DOM-based, meaning the malicious payload is executed as a result of client-side script processing, which can complicate detection and mitigation if not properly addressed in the plugin's code or through input sanitization and output encoding.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on WordPress websites that utilize the Meks Flexible Shortcodes plugin for content management and dynamic page generation. Successful exploitation can lead to unauthorized disclosure of sensitive user data, session token theft, and potential website defacement or redirection to phishing or malware distribution sites. This can damage organizational reputation, result in regulatory non-compliance (e.g., GDPR violations due to data leakage), and cause operational disruptions. Given the medium severity and requirement for user interaction, the risk is moderate but non-negligible, particularly for sectors with high web presence such as e-commerce, media, and public services. The DOM-based nature of the XSS also means that traditional server-side input validation may not be sufficient, increasing the complexity of defense. Additionally, the scope change indicates that the vulnerability could impact other components or user sessions beyond the immediate plugin context, amplifying potential damage.

1. Immediate mitigation should include disabling or removing the Meks Flexible Shortcodes plugin until a security patch is released. 2. Monitor official vendor channels and trusted security advisories for patch releases and apply updates promptly. 3. Implement Content Security Policy (CSP) headers with strict script-src directives to limit the execution of unauthorized scripts on affected web pages. 4. Employ web application firewalls (WAFs) with custom rules to detect and block suspicious input patterns targeting shortcode parameters. 5. Conduct thorough input sanitization and output encoding on all user-controllable inputs within the website, especially those processed by shortcodes, to prevent injection of malicious scripts. 6. Educate users and administrators about the risks of clicking on untrusted links that could trigger XSS attacks. 7. Perform regular security audits and penetration testing focusing on client-side vulnerabilities such as DOM-based XSS. 8. For organizations with high-risk profiles, consider isolating or sandboxing web components that use the vulnerable plugin to limit the impact of potential exploitation.