CVE-2026-23605 is a stored cross-site scripting vulnerability classified under CWE-79 affecting GFI Software's MailEssentials AI product, specifically versions prior to 22.4. The vulnerability resides in the Attachment Filtering rule creation workflow, where the parameter ctl00$ContentPlaceHolder1$pv1$TXB_RuleName accepts user input without proper neutralization. An authenticated user can inject malicious HTML or JavaScript code into this parameter on the /MailEssentials/pages/MailSecurity/attachmentchecking.aspx page. This input is stored persistently and later rendered in the management interface without adequate sanitization, allowing the execution of arbitrary scripts in the context of a logged-in administrator or user. Exploitation requires the attacker to have valid credentials and involves user interaction to inject the payload. The vulnerability could be leveraged to hijack sessions, perform unauthorized actions, or escalate privileges within the MailEssentials AI management console. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges required beyond authentication, and user interaction required, with limited confidentiality and integrity impact but no availability impact. No public exploits or active exploitation have been reported to date. The vulnerability highlights the importance of input validation and output encoding in web application workflows, especially in security management interfaces.

The primary impact of CVE-2026-23605 is the potential for attackers with authenticated access to execute arbitrary scripts within the MailEssentials AI management interface. This can lead to session hijacking, allowing attackers to impersonate administrators or other privileged users. Consequently, attackers could manipulate email security policies, disable protections, or exfiltrate sensitive configuration data. While the vulnerability does not directly affect email delivery or availability, compromising the management console could undermine the overall security posture of an organization's email infrastructure. Organizations relying on GFI MailEssentials AI for email threat protection may face increased risk of targeted attacks, especially if attackers gain initial access through phishing or credential compromise. The requirement for authentication and user interaction limits the ease of exploitation but does not eliminate risk, particularly in environments with weak credential management or insider threats. The vulnerability could also be used as a foothold for lateral movement within networks, potentially impacting broader organizational security.

To mitigate CVE-2026-23605, organizations should prioritize upgrading GFI MailEssentials AI to version 22.4 or later where the vulnerability is fixed. If immediate patching is not feasible, implement strict access controls to limit management interface access to trusted administrators only, ideally via VPN or zero-trust network segmentation. Enforce strong authentication mechanisms, including multi-factor authentication, to reduce the risk of credential compromise. Conduct regular audits of user accounts and permissions to detect unauthorized access. Additionally, apply web application firewall (WAF) rules to detect and block suspicious input patterns targeting the vulnerable parameter. Review and sanitize all user inputs in custom workflows and monitor logs for unusual activity related to rule creation or modification. Educate administrators about the risks of XSS and the importance of cautious input handling. Finally, consider isolating the management interface from general user networks to reduce exposure.