CVE-2025-53504 is a cross-site scripting (XSS) vulnerability identified in the Group-Office software developed by Intermesh BV. This vulnerability affects versions prior to 6.8.119 and 25.0.20 of Group-Office. XSS vulnerabilities occur when an application allows untrusted input to be included in web pages without proper validation or escaping, enabling attackers to inject malicious scripts that execute in the context of a victim's browser. In this case, exploitation of the vulnerability allows an attacker to execute arbitrary scripts in the user's browser session. The CVSS v3.0 base score is 5.4, indicating a medium severity level. The vector string (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) shows that the attack can be launched remotely over the network with low attack complexity, requires low privileges, and user interaction is necessary. The scope is changed, meaning the vulnerability affects resources beyond the initially vulnerable component. The impact affects confidentiality and integrity to a limited extent, with no impact on availability. No known exploits are currently reported in the wild. Group-Office is a web-based groupware and collaboration platform used for email, calendar, file sharing, and project management, often deployed in enterprise environments. The vulnerability could be leveraged to steal session cookies, perform actions on behalf of users, or deliver malware, potentially leading to unauthorized access or data leakage within affected organizations.

For European organizations using Group-Office, this vulnerability poses a risk of client-side attacks that could compromise user sessions and data confidentiality. Since Group-Office is used for collaboration and communication, successful exploitation could lead to unauthorized access to sensitive corporate information, internal communications, and project data. The requirement for user interaction (e.g., clicking a malicious link) somewhat limits the attack vector but does not eliminate risk, especially in environments where phishing attacks are common. The vulnerability's medium severity suggests that while it is not critical, it could be leveraged as part of a multi-stage attack chain. European organizations in sectors such as finance, government, healthcare, and legal services, which rely heavily on secure collaboration tools, could face reputational damage, regulatory penalties under GDPR for data breaches, and operational disruptions if attackers exploit this vulnerability to escalate privileges or exfiltrate data.

Organizations should prioritize upgrading Group-Office installations to version 6.8.119 or later, where the vulnerability is patched. In the absence of immediate patching, administrators should implement strict input validation and output encoding on all user-supplied data within the application, especially in areas exposed to user input. Employing Content Security Policy (CSP) headers can help mitigate the impact of XSS by restricting the execution of unauthorized scripts. User awareness training to recognize phishing and suspicious links can reduce the likelihood of user interaction with malicious payloads. Additionally, monitoring web application logs for unusual input patterns and anomalous user behaviors can help detect attempted exploitation. Network-level protections such as web application firewalls (WAFs) configured to detect and block XSS payloads can provide an additional layer of defense. Regular security assessments and penetration testing focused on web application vulnerabilities are recommended to identify and remediate similar issues proactively.