CVE-2025-11807 is a stored Cross-Site Scripting (XSS) vulnerability identified in the Mixlr Shortcode plugin for WordPress, affecting all versions up to and including 1.0.1. The vulnerability stems from insufficient input sanitization and output escaping of the 'url' attribute within the 'mixlr' shortcode. This flaw allows authenticated attackers with contributor-level privileges or higher to inject arbitrary JavaScript code into WordPress pages. Because the malicious script is stored persistently in the page content, it executes whenever any user accesses the compromised page, potentially leading to session hijacking, credential theft, defacement, or pivoting attacks within the affected site. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. The CVSS v3.1 base score is 6.4, reflecting a medium severity level, with an attack vector of network, low attack complexity, requiring privileges (PR:L), no user interaction, and a scope change (S:C). The impact affects confidentiality and integrity but not availability. No public exploits have been reported yet, but the vulnerability is significant due to the common use of WordPress and the Mixlr Shortcode plugin in content management. The vulnerability was published on October 22, 2025, and assigned by Wordfence. No official patches or updates are currently linked, indicating the need for vigilance and interim mitigations.

For European organizations, this vulnerability poses a moderate risk primarily to websites running WordPress with the Mixlr Shortcode plugin installed. The ability for contributors or higher privileged users to inject persistent malicious scripts can lead to unauthorized access to user sessions, theft of sensitive information, and potential defacement or reputational damage. Organizations relying on user-generated content or collaborative publishing are particularly vulnerable, as contributor-level users are often trusted to add content. The compromise of site integrity can also lead to further exploitation, including phishing attacks targeting visitors. Given the widespread use of WordPress across Europe, especially in sectors like media, education, and small to medium enterprises, the impact can be significant if not addressed. However, the requirement for authenticated access limits the attack surface somewhat, reducing the risk of mass exploitation. Nonetheless, the scope change in the CVSS vector indicates that the vulnerability can affect resources beyond the initially compromised component, increasing potential damage.

1. Immediately audit WordPress installations to identify the presence of the Mixlr Shortcode plugin and verify its version. 2. Restrict contributor-level permissions to trusted users only, and review user roles to minimize unnecessary privileges. 3. Implement strict input validation and output encoding on all user-supplied data, especially for shortcodes and custom attributes, either via plugin updates or custom hardening. 4. Deploy a Web Application Firewall (WAF) with rules to detect and block XSS payloads targeting the 'url' attribute or shortcode parameters. 5. Monitor website logs and user activity for unusual behavior indicative of exploitation attempts. 6. Encourage plugin developers or maintainers to release a patch promptly; until then, consider disabling the plugin if feasible. 7. Educate content contributors about the risks of injecting untrusted content and enforce content review workflows. 8. Regularly update WordPress core and all plugins to the latest versions to reduce exposure to known vulnerabilities.