CVE-2026-23607 is a stored cross-site scripting (XSS) vulnerability classified under CWE-79, found in GFI Software's MailEssentials AI product prior to version 22.4. The vulnerability resides in the Anti-Spam Whitelist management interface, specifically in the ctl00$ContentPlaceHolder1$pv1$txtDescription parameter on the Whitelist.aspx page. An authenticated user can inject arbitrary HTML or JavaScript code into this parameter, which is then stored persistently and rendered later in the management interface without proper neutralization or sanitization. This flaw allows malicious scripts to execute in the security context of other logged-in users, potentially enabling session hijacking, unauthorized actions, or privilege escalation within the administrative interface. The vulnerability requires the attacker to have authenticated access and some level of user interaction, which limits its exploitation scope. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges required beyond authentication, and user interaction is needed. The vulnerability impacts confidentiality and integrity moderately, with limited availability impact. No public exploits have been reported yet, but the presence of stored XSS in an administrative interface poses a significant risk if exploited. The lack of available patches at the time of publication necessitates immediate mitigation efforts by affected organizations.

The primary impact of CVE-2026-23607 is the potential compromise of administrative sessions and unauthorized actions within the MailEssentials AI management interface. Successful exploitation can lead to session hijacking, allowing attackers to impersonate legitimate administrators and modify security settings, such as whitelist entries, potentially weakening the organization's spam and malware defenses. This can result in increased exposure to phishing, malware delivery, or data exfiltration via email. The vulnerability also risks integrity by enabling attackers to inject malicious scripts that could alter the interface behavior or steal sensitive configuration data. Although availability impact is limited, the overall security posture of the affected email security gateway is degraded, increasing the risk of downstream attacks. Organizations relying on GFI MailEssentials AI for email protection, especially those with multiple administrators or remote management, face elevated risks. The medium CVSS score reflects moderate exploitability and impact, but the administrative nature of the interface raises the stakes for targeted attacks.

To mitigate CVE-2026-23607, organizations should first apply the official patch from GFI Software once available, upgrading MailEssentials AI to version 22.4 or later. Until patches are deployed, administrators should restrict access to the Anti-Spam Whitelist management interface to trusted personnel only and enforce strong authentication mechanisms, such as multi-factor authentication, to reduce the risk of unauthorized access. Implement strict input validation and output encoding on the txtDescription parameter to neutralize potentially malicious HTML or JavaScript content. Employ web application firewalls (WAFs) with custom rules to detect and block suspicious payloads targeting the vulnerable parameter. Regularly audit whitelist entries for suspicious or unexpected content. Additionally, monitor administrative sessions for unusual activity indicative of session hijacking or privilege abuse. Educate administrators about the risks of stored XSS and safe input handling practices. Finally, maintain up-to-date backups of configuration data to enable recovery in case of compromise.