CVE-2026-1435 is a critical security vulnerability identified in Graylog Web Interface version 2.2.3, classified under CWE-613 (Insufficient Session Expiration). Graylog is a popular log management and analysis platform used by organizations to monitor IT infrastructure and security events. The vulnerability arises because the application generates a new sessionId on each user login but does not invalidate previously issued session identifiers. Consequently, old session tokens remain valid and can be reused by an attacker who has obtained them, enabling unauthorized access to the Graylog web interface and API. This flaw affects the confidentiality and integrity of user accounts and the data accessible through the Graylog platform. Exploitation requires network access to the Graylog service, typically on port 9000 or via HTTP/S endpoints, but does not require user interaction or prior authentication, making it highly exploitable. The CVSS 4.0 base score of 9.3 reflects the vulnerability’s critical impact, with high confidentiality and integrity impact, low attack complexity, and no privileges or user interaction required. Although no public exploits are currently known, the vulnerability poses a significant risk to organizations relying on Graylog for security monitoring and log management. The lack of session invalidation after new logins can lead to session hijacking, persistent unauthorized access, and potential manipulation or exfiltration of sensitive log data. This can undermine incident response capabilities and expose organizations to further attacks. The vulnerability was published on February 18, 2026, and assigned by INCIBE. No official patches are listed yet, indicating that organizations must apply interim mitigations until a fix is available.

For European organizations, the impact of CVE-2026-1435 is substantial, particularly for those using Graylog 2.2.3 to monitor critical infrastructure, financial systems, or government networks. Unauthorized access via reused session tokens can lead to compromise of sensitive log data, which may include security events, user activity, and system alerts. This undermines the integrity and reliability of security monitoring, potentially delaying detection of other attacks. Attackers could manipulate logs to cover their tracks or gain deeper access to network resources through the Graylog interface. The vulnerability’s ease of exploitation and lack of required authentication increase the risk of widespread abuse, especially in environments where Graylog interfaces are exposed to internal or external networks. The confidentiality breach could expose personal data or intellectual property, raising compliance concerns under GDPR and other European data protection regulations. Operational disruption may occur if attackers alter or delete logs, impacting forensic investigations and incident response. The threat is heightened in sectors with high regulatory scrutiny and critical infrastructure, such as energy, finance, healthcare, and government agencies.

Immediate mitigation steps include restricting network access to the Graylog web interface and API endpoints by implementing strict firewall rules and network segmentation to limit exposure to trusted users only. Organizations should enforce multi-factor authentication (MFA) on Graylog accounts to reduce the risk of session token theft leading to unauthorized access. Monitoring for unusual session activity and implementing session timeout policies can help detect and limit the impact of reused session tokens. Administrators should review and revoke any suspicious or inactive sessions manually if the Graylog interface allows it. Until an official patch is released, consider deploying Web Application Firewalls (WAFs) with custom rules to detect and block reuse of old session tokens. Regularly update Graylog to the latest versions once patches addressing this vulnerability become available. Additionally, educate users on secure session management practices and the risks of session token leakage. Conduct thorough audits of Graylog access logs to identify potential exploitation attempts. Finally, coordinate with Graylog vendor support for updates and guidance on secure configuration.