CVE-2023-53891 identifies a stored cross-site scripting vulnerability in Blackcat CMS version 1.4. This vulnerability arises from improper neutralization of input during web page generation, specifically allowing authenticated users to inject malicious JavaScript payloads into page content via the page modification interface. When other users access the compromised pages, the injected scripts execute in their browsers, enabling attackers to perform actions such as session hijacking, stealing cookies or credentials, or conducting further attacks within the context of the victim's session. The vulnerability requires the attacker to have authenticated access to the CMS, which limits exploitation to users with some level of privilege. User interaction is necessary for the payload to execute, as it triggers when another user views the infected page. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required beyond authenticated user (PR:L), and user interaction required (UI:P). The impact on confidentiality and integrity is low to limited, with no direct availability impact. No patches or known exploits are currently publicly available, but the vulnerability is published and should be addressed promptly. The vulnerability is typical of stored XSS issues in content management systems where input sanitization and output encoding are insufficient or missing during page rendering.

For European organizations using Blackcat CMS 1.4, this vulnerability poses a risk primarily to the confidentiality and integrity of user sessions and data. Attackers with authenticated access can embed malicious scripts that execute in other users' browsers, potentially leading to credential theft, session hijacking, or unauthorized actions performed under the victim's identity. This can compromise sensitive information and disrupt trust in web applications. While the vulnerability does not directly affect system availability, successful exploitation could lead to further attacks or data leakage. Organizations with multiple content editors or users with CMS access are at higher risk. The medium severity rating reflects the need for authentication and user interaction, which somewhat limits the attack surface but does not eliminate risk. Given the widespread use of CMS platforms in Europe for public-facing websites and intranets, exploitation could impact business operations, reputation, and compliance with data protection regulations such as GDPR if personal data is exposed.

1. Apply patches or updates from Blackcat CMS vendor as soon as they become available to address CVE-2023-53891. 2. Until patches are released, restrict CMS user permissions to the minimum necessary, limiting page modification rights to trusted users only. 3. Implement strict input validation and output encoding on all user-supplied content within the CMS, especially in the page modification interface, to neutralize potentially malicious scripts. 4. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers accessing the CMS pages. 5. Conduct regular security audits and code reviews focusing on input handling and output rendering in the CMS. 6. Monitor CMS logs and user activity for unusual behavior indicative of attempted exploitation. 7. Educate CMS users about the risks of XSS and safe content editing practices. 8. Consider deploying web application firewalls (WAF) with rules to detect and block XSS payloads targeting the CMS.