CVE-2025-49137 is a high-severity cross-site scripting (XSS) vulnerability affecting the haxtheweb 'issues' product, specifically versions prior to 11.0.0. The vulnerability arises from improper neutralization of user input during web page generation, classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). In this case, the haxtheweb CMS PHP backend allows users to manage microsites by submitting data to the 'saveNode' and 'saveManifest' endpoints. These endpoints accept user input that is stored within the site's JSON schema and later rendered on the generated HAX site. Although the application blocks the use of explicit <script> tags, it fails to sanitize other HTML elements that can execute JavaScript, such as event handlers (e.g., onclick) or other executable attributes. This flaw enables an attacker with at least low privileges (PR:L) and no user interaction (UI:N) to inject arbitrary JavaScript code, which can execute in the context of other users viewing the affected microsite. The CVSS 3.1 score of 8.5 reflects the network attack vector (AV:N), low attack complexity (AC:L), and the scope change (S:C), indicating that the vulnerability can affect resources beyond the initially compromised component. The impact on confidentiality is high (C:H) due to potential theft of session tokens or sensitive data, integrity impact is low (I:L) as the attacker can manipulate client-side data, and availability is not affected (A:N). No known exploits are currently reported in the wild, but the vulnerability is publicly disclosed and fixed in version 11.0.0. Organizations using haxtheweb CMS versions prior to 11.0.0 are at risk of client-side attacks that can lead to session hijacking, phishing, or unauthorized actions performed on behalf of users.

For European organizations, this vulnerability poses significant risks, especially for those relying on haxtheweb CMS to manage public-facing microsites or internal portals. Exploitation could lead to the compromise of user sessions, leakage of sensitive information, and unauthorized actions performed in the context of authenticated users. This is particularly critical for sectors handling personal data under GDPR regulations, as data breaches could result in regulatory penalties and reputational damage. Additionally, organizations in finance, healthcare, and government sectors are at heightened risk due to the sensitive nature of their data and the potential for targeted attacks leveraging this vulnerability. The ability to execute arbitrary JavaScript without user interaction and with low privileges increases the likelihood of automated exploitation attempts. Furthermore, the scope change in the vulnerability means that an attacker could leverage this flaw to affect other components or users beyond the initially targeted microsite, amplifying the potential damage.

To mitigate this vulnerability, European organizations should immediately upgrade haxtheweb 'issues' to version 11.0.0 or later, where the issue is resolved. If immediate upgrading is not feasible, organizations should implement strict input validation and sanitization on the 'saveNode' and 'saveManifest' endpoints, ensuring that all user-supplied HTML content is sanitized to remove executable attributes and disallowed tags beyond just <script>. Employing a robust HTML sanitizer library that enforces a whitelist of safe tags and attributes is recommended. Additionally, implementing Content Security Policy (CSP) headers can help mitigate the impact by restricting the execution of inline scripts and external resources. Organizations should also conduct thorough code reviews and penetration testing focused on XSS vectors within their haxtheweb deployments. Monitoring web application logs for suspicious inputs and anomalous behavior related to these endpoints can aid in early detection of exploitation attempts. Finally, educating developers and administrators about secure coding practices and the risks of improper input handling will help prevent similar vulnerabilities in the future.