CVE-2025-11189 identifies a reflected cross-site scripting (XSS) vulnerability in Synchroweb's Kiwire Captive Portal version 3.6. The vulnerability arises from improper neutralization of input during web page generation, specifically within the login-url parameter. When a user accesses a specially crafted URL containing malicious JavaScript code embedded in this parameter, the portal reflects this input without proper sanitization or encoding, causing the browser to execute the injected script. This type of XSS attack can be leveraged by attackers to perform various malicious actions, including stealing session cookies, capturing user credentials, performing actions on behalf of the user, or redirecting users to phishing or malware-laden websites. Since the vulnerability is reflected, it requires the victim to click or be redirected to a malicious link. The vulnerability does not require authentication, increasing its risk profile. Although no known exploits are currently reported in the wild and no patches have been published, the presence of this vulnerability in a captive portal—a common access point for public and enterprise Wi-Fi users—makes it a critical concern. The lack of a CVSS score necessitates an independent severity assessment based on the vulnerability's characteristics and potential impact.

For European organizations, especially those operating public or guest Wi-Fi networks such as hotels, airports, universities, and cafes, this vulnerability poses significant risks. Exploitation could lead to unauthorized access to user sessions, theft of sensitive credentials, and redirection to malicious sites, undermining user trust and potentially exposing organizations to regulatory penalties under GDPR if personal data is compromised. The captive portal is often the first point of interaction for users connecting to a network, making it a high-value target for attackers seeking to intercept or manipulate user traffic. Additionally, successful exploitation could facilitate further attacks within the network or enable lateral movement. The reputational damage and potential financial losses from such incidents could be substantial, particularly in sectors reliant on customer trust and data privacy compliance.

Immediate mitigation should focus on implementing strict input validation and output encoding for the login-url parameter to ensure that any user-supplied data is properly sanitized before being reflected in the web page. Organizations should monitor network traffic for suspicious URLs targeting the captive portal and educate users about the risks of clicking unknown links. Deploying web application firewalls (WAFs) with rules to detect and block XSS payloads targeting the login-url parameter can provide an additional layer of defense. Until an official patch is released by Synchroweb, consider restricting access to the captive portal management interface and limiting exposure of the vulnerable parameter where feasible. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities. Finally, organizations should maintain an incident response plan to quickly address any exploitation attempts.