CVE-2026-23608 is a stored cross-site scripting vulnerability classified under CWE-79 affecting GFI Software's MailEssentials AI versions prior to 22.4. The vulnerability arises from improper neutralization of input during web page generation in the Mail Monitoring rule creation endpoint. Specifically, an authenticated user can submit malicious HTML or JavaScript code within the JSON "name" field sent to the endpoint /MailEssentials/pages/MailSecurity/MailMonitoring.aspx/Save. This input is stored persistently and later rendered in the management interface without adequate sanitization or encoding, allowing the injected script to execute in the context of any logged-in user viewing the interface. The attack vector requires network access and user authentication but no elevated privileges, and user interaction is needed to trigger the malicious script. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no authentication required (AT:N) but privileges required (PR:L), user interaction required (UI:P), and low impact on confidentiality and integrity but no impact on availability. This vulnerability could enable attackers to perform actions such as session hijacking, credential theft, or unauthorized actions within the management interface, potentially leading to broader compromise of the email security environment. No public exploits have been reported yet, but the vulnerability's presence in a widely used email security product makes it a notable risk. The lack of a patch link suggests that remediation may require vendor updates or manual mitigations.

The vulnerability allows an authenticated attacker to inject and execute arbitrary scripts in the management interface of GFI MailEssentials AI, potentially leading to session hijacking, theft of administrative credentials, or unauthorized actions within the email security platform. This can undermine the integrity and confidentiality of the email security environment, possibly allowing attackers to bypass security controls, manipulate email filtering rules, or gain further footholds in the network. Organizations relying on MailEssentials AI for email protection could face increased risk of targeted attacks, data breaches, or disruption of email security operations. Since the vulnerability requires authentication, the risk is somewhat mitigated but remains significant in environments with many users or weak access controls. The medium CVSS score reflects moderate impact and exploitability, but the potential for lateral movement or privilege escalation within the management interface elevates the threat. The absence of known exploits reduces immediate risk but does not preclude future exploitation.

1. Upgrade GFI MailEssentials AI to version 22.4 or later once available, as this version addresses the vulnerability. 2. Until patching is possible, restrict access to the management interface to trusted administrators only and enforce strong authentication mechanisms such as multi-factor authentication (MFA). 3. Implement strict input validation and output encoding on the Mail Monitoring rule creation endpoint to neutralize HTML and JavaScript content in user-supplied fields. 4. Monitor logs for suspicious activity related to rule creation or modifications in the Mail Monitoring interface. 5. Conduct regular security audits and penetration testing focusing on web interface vulnerabilities. 6. Educate administrators about the risks of XSS and encourage cautious handling of rule creation inputs. 7. Consider network segmentation to limit access to the management interface from untrusted networks. 8. Employ web application firewalls (WAFs) with rules to detect and block XSS payloads targeting the affected endpoint.