CVE-2026-23794 is a reflected Cross-site Scripting (XSS) vulnerability classified under CWE-79, found in the Enduser Login page of Apache Syncope, an open-source identity management system developed by the Apache Software Foundation. The vulnerability arises due to improper neutralization of input during web page generation, allowing malicious input to be reflected back in the HTTP response without adequate sanitization or encoding. This flaw affects Apache Syncope versions 3.0 through 3.0.15 and 4.0 through 4.0.3. An attacker can exploit this by crafting a malicious URL containing a payload that, when clicked by a legitimate user, executes arbitrary JavaScript code in the context of the victim's browser session. This can lead to theft of user credentials or session tokens, enabling unauthorized access to the victim's account. The attack requires social engineering to lure the user into clicking the malicious link and logging into the Syncope Enduser portal. The vulnerability does not require prior authentication but does require user interaction. The Apache Software Foundation has addressed this issue in versions 3.0.16 and 4.0.4 by implementing proper input validation and output encoding on the login page. No public exploits or active exploitation campaigns have been reported to date, but the risk remains significant due to the sensitive nature of identity management systems and the potential for credential compromise.

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of user credentials managed through Apache Syncope. Identity management systems are critical infrastructure components that control access to various enterprise resources. Exploitation could lead to unauthorized access, lateral movement within networks, and potential data breaches. Given the GDPR and other stringent data protection regulations in Europe, a compromise resulting from this vulnerability could lead to regulatory penalties and reputational damage. Organizations in sectors such as finance, healthcare, government, and telecommunications, which often rely on robust identity management solutions, are particularly at risk. The ease of exploitation through social engineering increases the threat, especially in environments with less user security awareness. Although no known exploits are currently active, the vulnerability's presence in widely used versions means that unpatched systems remain exposed.

European organizations should immediately upgrade Apache Syncope installations to versions 3.0.16 or 4.0.4, which contain the official patches for this vulnerability. In addition to patching, organizations should implement strict Content Security Policies (CSP) to restrict the execution of unauthorized scripts in browsers. Web Application Firewalls (WAFs) can be configured to detect and block suspicious input patterns indicative of reflected XSS attempts targeting the login page. User awareness training should emphasize the risks of clicking on unsolicited or suspicious links, especially those purporting to lead to login portals. Logging and monitoring should be enhanced to detect anomalous login attempts or unusual URL parameters. For environments where immediate patching is not feasible, consider restricting access to the Syncope Enduser portal via VPN or IP whitelisting to reduce exposure. Regular security assessments and penetration tests should include checks for XSS vulnerabilities in critical web applications.