CVE-2025-5540 is a stored Cross-Site Scripting (XSS) vulnerability affecting the Event RSVP and Simple Event Management Plugin developed by emarket-design for WordPress. This vulnerability exists in all versions up to and including 4.1.0 due to improper neutralization of input during web page generation, specifically within the plugin's 'emd_mb_meta' shortcode. The root cause is insufficient sanitization and output escaping of user-supplied attributes, which allows an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript code into pages generated by the plugin. Because the malicious script is stored persistently, it executes every time any user accesses the compromised page, potentially leading to session hijacking, privilege escalation, or unauthorized actions performed on behalf of the victim. The vulnerability has a CVSS 3.1 base score of 6.4, indicating a medium severity level. The attack vector is network-based (remote), requires low attack complexity, and privileges at the contributor level, but no user interaction is needed for exploitation. The scope is changed, meaning the vulnerability affects resources beyond the initially vulnerable component. No known exploits are currently reported in the wild, and no official patches have been linked yet. This vulnerability falls under CWE-79, which is a common and well-understood class of web application security flaws related to improper input validation and output encoding, making it a significant risk in web environments where user-generated content is processed and displayed.

For European organizations using WordPress websites with the Event RSVP and Simple Event Management Plugin, this vulnerability poses a moderate risk. Exploitation could lead to unauthorized script execution in the context of the affected website, enabling attackers to steal session cookies, deface websites, redirect users to malicious sites, or perform actions with the privileges of logged-in users. This can result in reputational damage, data leakage, and potential compliance violations under GDPR if personal data is compromised. Organizations relying on these plugins for event management, especially those handling sensitive or regulated data, may face operational disruptions. Since the vulnerability requires contributor-level access, insider threats or compromised accounts increase risk. The persistent nature of stored XSS means that once injected, the malicious payload can affect multiple users over time, amplifying impact. Although no known exploits are currently active, the widespread use of WordPress in Europe and the popularity of event management plugins increase the likelihood of targeted attacks, especially against organizations with public-facing event registration portals.

Beyond general advice to update plugins, European organizations should: 1) Immediately audit WordPress sites for the presence of the vulnerable Event RSVP and Simple Event Management Plugin and restrict contributor-level access to trusted users only. 2) Implement Web Application Firewalls (WAFs) with custom rules to detect and block suspicious script injections in the 'emd_mb_meta' shortcode parameters. 3) Conduct manual or automated code reviews and sanitization checks on user-generated content fields related to event management to identify and neutralize malicious inputs. 4) Employ Content Security Policy (CSP) headers to restrict execution of unauthorized scripts on affected pages. 5) Monitor logs and user activity for unusual behavior indicative of exploitation attempts, such as unexpected script payloads or anomalous contributor actions. 6) Prepare incident response plans specifically addressing stored XSS scenarios, including rapid content cleanup and user notification procedures. 7) Engage with plugin vendors or the WordPress community to track patch releases and apply updates promptly once available. 8) Educate content contributors on secure input practices and the risks of injecting untrusted data into web pages.