CVE-2026-23616 is a stored cross-site scripting (XSS) vulnerability classified under CWE-79, affecting GFI Software's MailEssentials AI product versions prior to 22.4. The vulnerability resides in the Anti-Spoofing configuration page, specifically in the ctl00$ContentPlaceHolder1$AntiSpoofingGeneral1$TxtSmtpDesc parameter of the /MailEssentials/pages/MailSecurity/AntiSpoofing.aspx endpoint. An authenticated user with access to this interface can inject malicious HTML or JavaScript code into this parameter. Because the input is improperly neutralized during web page generation, the injected script is stored persistently and executed when other authenticated users access the management interface. This can lead to unauthorized script execution within the context of the victim's session, enabling potential session hijacking, privilege escalation, or unauthorized configuration changes. The vulnerability requires the attacker to have valid credentials (authenticated user) and some user interaction (accessing the affected page). The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:L), user interaction required (UI:P), and low impact on confidentiality, integrity, and availability (VC:L, VI:L, VA:N). No public exploits are known at this time, but the vulnerability poses a risk in environments where multiple administrators or users access the MailEssentials AI management interface. The flaw highlights insufficient input validation and output encoding in the web application’s anti-spoofing configuration component.

The impact of CVE-2026-23616 is primarily on the confidentiality and integrity of the MailEssentials AI management interface. Successful exploitation allows an authenticated attacker to execute arbitrary scripts in the context of other logged-in users, potentially leading to session hijacking, theft of administrative credentials, or unauthorized changes to email security configurations. This can undermine the effectiveness of the email security solution, potentially allowing phishing, spoofing, or malware delivery to bypass defenses. While availability impact is low, the compromise of administrative accounts or configurations can have cascading effects on organizational email security posture. Organizations relying on MailEssentials AI for email threat protection may face increased risk of targeted attacks or insider threats exploiting this vulnerability. The requirement for authentication limits exposure to internal or credentialed attackers but does not eliminate risk, especially in environments with multiple administrators or weak credential management.

To mitigate CVE-2026-23616, organizations should upgrade GFI MailEssentials AI to version 22.4 or later where the vulnerability is fixed. If immediate patching is not possible, restrict access to the Anti-Spoofing configuration page to the minimum necessary set of trusted administrators using network segmentation, VPNs, or firewall rules. Implement strong authentication mechanisms such as multi-factor authentication (MFA) to reduce the risk of credential compromise. Regularly audit user accounts and permissions to ensure only authorized personnel have access to the management interface. Employ web application firewalls (WAFs) with custom rules to detect and block suspicious input patterns targeting the vulnerable parameter. Monitor logs for unusual activity related to the Anti-Spoofing page and investigate any anomalies promptly. Educate administrators about the risks of XSS and safe handling of configuration inputs. Finally, validate and sanitize all user inputs in custom scripts or integrations interacting with MailEssentials AI to prevent similar vulnerabilities.