CVE-2026-1439 is a reflected Cross-Site Scripting (XSS) vulnerability identified in Graylog Web Interface version 2.2.3. The vulnerability stems from improper neutralization of input during web page generation, specifically a failure to sanitize and escape URL segments embedded directly into HTML responses. The affected endpoint '/alerts/' includes parts of the URL in the response without output encoding, allowing attackers to inject arbitrary JavaScript code. When a victim user accesses a specially crafted URL, the malicious script executes in their browser context, potentially enabling session manipulation or theft of sensitive information accessible via the browser session. The vulnerability does not require authentication, increasing its risk, but does require user interaction to trigger. The CVSS 4.0 vector indicates network attack vector, low attack complexity, no privileges or user interaction required for the attack to succeed, but user interaction is marked as required (UI:P). The impact on confidentiality and integrity is limited but non-negligible, as session context manipulation can lead to further attacks. No public exploits have been reported yet, but the presence of this vulnerability in a widely used log management tool like Graylog raises concerns for organizations relying on it for security monitoring and operational insights.

For European organizations, the exploitation of this XSS vulnerability could lead to unauthorized script execution within the browsers of users accessing the Graylog Web Interface. This may result in session hijacking, unauthorized actions performed on behalf of the user, or exposure of sensitive session data. Given Graylog's role in log management and security monitoring, compromise of its web interface could undermine trust in security operations and incident response capabilities. Organizations in sectors with strict data protection regulations (e.g., GDPR) could face compliance risks if user data is exposed or manipulated. Additionally, attackers could leverage this vulnerability as a foothold for further attacks within the network if administrative users are targeted. The medium severity rating reflects a moderate risk, but the potential impact is amplified in environments where Graylog is critical for security visibility.

1. Immediately restrict access to the Graylog Web Interface to trusted networks and users to reduce exposure. 2. Implement strict input validation and output encoding on all user-controllable inputs, especially URL parameters, to prevent injection of malicious scripts. 3. Monitor web server logs for suspicious requests targeting the '/alerts/' endpoint with unusual URL patterns. 4. Educate users about the risks of clicking unknown or suspicious links, particularly those purporting to lead to Graylog dashboards. 5. Apply any available patches or updates from Graylog addressing this vulnerability as soon as they are released. 6. Consider deploying Web Application Firewalls (WAFs) with rules to detect and block reflected XSS attempts targeting Graylog interfaces. 7. Conduct regular security assessments and penetration tests focusing on web interface vulnerabilities. 8. If upgrading is not immediately possible, implement custom output encoding in reverse proxies or web server configurations to mitigate script injection risks.