CVE-2025-5366 is a high-severity stored Cross-Site Scripting (XSS) vulnerability affecting ManageEngine Exchange Reporter Plus, specifically versions 5722 and below. The vulnerability arises from improper neutralization of input during web page generation (CWE-79), allowing malicious actors to inject and store arbitrary scripts within the 'Folder-wise read mails with subject report' feature. When a user accesses this report, the malicious script executes in their browser context, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The CVSS v3.1 score of 8.1 reflects the vulnerability's network exploitable nature (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The impact on confidentiality and integrity is high, while availability is not affected. No known exploits are currently reported in the wild, and no official patches have been linked yet. This vulnerability is critical for organizations relying on ManageEngine Exchange Reporter Plus for monitoring Microsoft Exchange environments, as it can be leveraged to compromise administrative accounts or spread malware within enterprise networks.

For European organizations, the impact of CVE-2025-5366 can be significant due to the widespread use of ManageEngine products in IT infrastructure management and Exchange monitoring. Exploitation could lead to unauthorized access to sensitive email metadata and reports, potentially exposing confidential communication patterns and organizational structure. Attackers could leverage the stored XSS to escalate privileges or move laterally within the network, compromising additional systems. Given the vulnerability requires user interaction, targeted phishing or social engineering campaigns could be used to trick administrators or analysts into triggering the malicious payload. This risk is heightened in sectors with strict data protection regulations such as GDPR, where data breaches can result in heavy fines and reputational damage. Furthermore, disruption or manipulation of Exchange reporting could impair incident response and compliance monitoring, critical for regulated industries like finance, healthcare, and government agencies across Europe.

Organizations should immediately audit their ManageEngine Exchange Reporter Plus installations to identify affected versions (5722 and below). Until an official patch is released, administrators should implement strict input validation and output encoding on the affected report generation components, if possible, via custom scripting or web application firewalls (WAF) that can detect and block malicious payloads. Restrict access to the Exchange Reporter Plus web interface to trusted IP ranges and enforce multi-factor authentication (MFA) to reduce the risk of exploitation. Security teams should increase monitoring for unusual activities in the reporting tool and conduct user awareness training focused on recognizing phishing attempts that could trigger the XSS payload. Additionally, consider isolating the reporting tool in a segmented network zone to limit lateral movement in case of compromise. Regularly check for vendor updates and apply patches promptly once available.