CVE-2025-53835 is a critical cross-site scripting (XSS) vulnerability affecting the xwiki-rendering component of the XWiki platform, specifically versions from 5.4.5 up to but not including 14.10. XWiki Rendering is responsible for converting textual input in various syntaxes, such as wiki syntax or HTML, into output formats like XHTML. The vulnerability arises because the XHTML syntax depends on the `xdom+xml/current` syntax, which allows the creation of raw blocks that can embed arbitrary HTML and JavaScript content. This flaw enables an attacker with edit permissions—such as users who can modify their own profile documents—to inject malicious scripts that execute in the context of other users viewing the affected pages. The vulnerability is rooted in improper neutralization of input during web page generation (CWE-79), leading to the potential compromise of confidentiality, integrity, and availability of the application and its users. The issue was addressed in version 14.10 by removing the dependency on the vulnerable `xdom+xml/current` syntax from the XHTML syntax. However, the `xdom+xml` syntax itself remains vulnerable but is primarily intended for testing and is not commonly used in production environments. There are no known workarounds other than upgrading to a fixed version. The CVSS v3.1 base score is 9.1, reflecting a critical severity with network attack vector, low attack complexity, requiring privileges to edit content, user interaction, and a scope change that impacts confidentiality, integrity, and availability.

For European organizations using XWiki versions between 5.4.5 and 14.10, this vulnerability poses a significant risk. Attackers who gain edit access—often granted to authenticated users such as employees or collaborators—can inject malicious scripts that execute in the browsers of other users. This can lead to session hijacking, credential theft, unauthorized actions performed on behalf of users, and potential spread of malware within the organization. Given that XWiki is often used for internal documentation, knowledge sharing, and collaboration, exploitation could result in leakage of sensitive corporate information, disruption of business processes, and erosion of trust in internal systems. The critical severity and ease of exploitation (low complexity) mean that even moderately skilled attackers could leverage this vulnerability. The lack of known workarounds other than upgrading increases the urgency for affected organizations to patch promptly. Additionally, the scope change indicates that the vulnerability can affect components beyond the initially compromised user, amplifying the potential damage.

The primary and most effective mitigation is to upgrade all affected XWiki instances to version 14.10 or later, where the vulnerable dependency has been removed. Organizations should audit their XWiki deployments to identify versions in the vulnerable range and plan immediate upgrades. Since the `xdom+xml` syntax remains vulnerable but is rarely used, administrators should verify that this syntax is not enabled or used in production environments. Access controls should be reviewed and tightened to limit edit permissions strictly to trusted users, reducing the risk of malicious content injection. Implementing Content Security Policy (CSP) headers can help mitigate the impact of XSS by restricting the execution of unauthorized scripts. Additionally, monitoring and logging user edits and page content changes can help detect suspicious activity early. Regular security training for users with edit privileges can reduce the risk of insider threats or accidental introduction of malicious content. Finally, organizations should consider deploying web application firewalls (WAFs) with rules tuned to detect and block XSS payloads targeting XWiki.