CVE-2023-53891 is a stored cross-site scripting vulnerability identified in Blackcat CMS version 1.4. The vulnerability arises from improper neutralization of input during web page generation, specifically in the page modification interface where authenticated users can insert malicious JavaScript payloads into page content. These scripts are stored persistently and executed in the browsers of other users who view the compromised pages, enabling attackers to perform actions such as session hijacking, cookie theft, or redirecting users to malicious sites. The vulnerability requires the attacker to have authenticated access to the CMS, which limits exploitation to users with some level of privileges. However, the attack does not require elevated privileges beyond authentication, and no user interaction beyond viewing the infected page is necessary for the payload to execute. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required beyond authentication (PR:L), user interaction required (UI:P), and low impact on confidentiality, integrity, and availability (VC:L, VI:L, VA:N). The vulnerability is classified as medium severity with a CVSS score of 5.1. No patches or known exploits are currently publicly available, but the risk remains significant due to the potential for lateral movement and data theft within affected organizations.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of web content and user sessions within Blackcat CMS environments. Attackers exploiting this flaw could hijack user sessions, steal credentials, or inject malicious content that damages organizational reputation or leads to further compromise. Since the vulnerability requires authenticated access, insider threats or compromised user accounts are the most likely vectors. The impact is heightened in organizations relying on Blackcat CMS for public-facing or internal web portals, especially where sensitive information or critical business functions are managed. Additionally, the persistent nature of stored XSS means that multiple users can be affected over time, increasing the potential damage. The medium severity rating suggests moderate risk, but targeted attacks against high-value European entities using Blackcat CMS could have significant operational and reputational consequences.

European organizations should immediately assess their use of Blackcat CMS version 1.4 and plan to upgrade to a patched version once available. In the absence of an official patch, organizations should implement strict input validation and output encoding on all user-supplied content within the CMS, especially in the page modification interface. Restricting CMS access to trusted users and enforcing strong authentication mechanisms, such as multi-factor authentication, can reduce the risk of exploitation. Regularly auditing user accounts and permissions to minimize the number of users with modification rights is critical. Additionally, implementing Content Security Policy (CSP) headers can help mitigate the impact of injected scripts by restricting the execution of unauthorized JavaScript. Monitoring web logs for unusual activity and scanning CMS content for injected scripts can aid in early detection. Finally, educating CMS users about the risks of XSS and safe content management practices will further reduce exposure.