CVE-2025-53490 is a Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the CampaignEvents extension of the Wikimedia Foundation's Mediawiki software. Specifically, this vulnerability exists in versions 1.43.x prior to 1.43.2. The issue arises due to improper neutralization of input during web page generation, allowing malicious actors to inject and execute arbitrary scripts in the context of the affected Mediawiki instance. The vulnerability has a CVSS v3.1 base score of 5.6, indicating a medium severity level. The vector string (AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L) suggests that the attack can be launched remotely over the network without requiring privileges or user interaction, but with high attack complexity. The impact includes limited confidentiality, integrity, and availability losses. Although no known exploits are currently reported in the wild, the presence of this vulnerability in a widely used wiki platform extension poses a risk of script injection attacks that could lead to session hijacking, defacement, or redirection to malicious sites. The CampaignEvents extension is used to manage and display campaign-related events within Mediawiki, so the vulnerability likely affects pages that render user-supplied or external input without proper sanitization. This flaw could be exploited by attackers to inject malicious JavaScript code that executes in the browsers of users visiting the affected wiki pages, potentially compromising user data or enabling further attacks within the user session context.

For European organizations using Mediawiki with the CampaignEvents extension, this vulnerability could lead to unauthorized disclosure of sensitive information, manipulation of displayed content, or disruption of service availability. Given Mediawiki's popularity in public and private knowledge bases, including governmental, educational, and corporate environments, exploitation could undermine trust in information integrity and confidentiality. Attackers could leverage this XSS flaw to steal authentication tokens, perform phishing attacks, or escalate privileges within the affected environment. The medium severity rating reflects that while the vulnerability does not allow direct system compromise or remote code execution, the potential for user session compromise and data leakage remains significant. Organizations relying on Mediawiki for collaborative documentation or public information dissemination may face reputational damage and operational disruption if this vulnerability is exploited. Additionally, the lack of user interaction required for exploitation increases the risk of automated attacks targeting vulnerable instances.

To mitigate this vulnerability, European organizations should promptly upgrade the CampaignEvents extension to version 1.43.2 or later, where the issue is resolved. If immediate patching is not feasible, organizations should implement strict input validation and output encoding on all user-supplied data rendered by the CampaignEvents extension. Employing Content Security Policy (CSP) headers can help restrict the execution of unauthorized scripts. Regularly auditing Mediawiki extensions for security updates and disabling unused or unnecessary extensions reduces the attack surface. Network-level protections such as Web Application Firewalls (WAFs) configured to detect and block XSS payloads can provide an additional layer of defense. Furthermore, organizations should educate users about the risks of XSS and encourage cautious behavior when interacting with wiki content. Monitoring logs for unusual activity related to the CampaignEvents extension can aid in early detection of exploitation attempts.