CVE-2026-26940 is a vulnerability classified under CWE-1284 (Improper Validation of Specified Quantity in Input) found in the Timelion visualization plugin of Elastic Kibana. Timelion allows users to create time series visualizations using expressions. The flaw arises because the plugin does not properly validate the quantity values specified in these expressions, enabling an authenticated user to submit a specially crafted Timelion expression that overwrites internal series data properties with an excessively large quantity. This leads to excessive memory allocation, which can cause a denial of service (DoS) condition by exhausting system resources or crashing the Kibana service. The vulnerability requires authentication but no additional user interaction, and it affects Kibana versions 8.0.0, 9.0.0, and 9.3.0. The CVSS v3.1 base score is 6.5, reflecting a medium severity level with network attack vector, low attack complexity, and no confidentiality or integrity impact but high availability impact. No patches were linked at the time of publication, and no known exploits have been reported in the wild. This vulnerability highlights the risk of insufficient input validation in complex visualization plugins that process user-supplied expressions.

The primary impact of CVE-2026-26940 is denial of service, which can disrupt the availability of Kibana dashboards and analytics services that rely on the Timelion plugin. Organizations using affected Kibana versions may experience service outages or degraded performance, potentially affecting monitoring, alerting, and operational visibility. Since Kibana is widely used for log analysis, security monitoring, and business intelligence, such disruptions can delay incident response and decision-making. The vulnerability does not compromise data confidentiality or integrity, but the loss of availability can have cascading effects on operational continuity. Attackers with valid credentials can exploit this flaw remotely, increasing the risk in environments where user access controls are weak or compromised. The absence of known exploits reduces immediate risk, but the medium severity score and ease of exploitation warrant proactive mitigation. Enterprises with large-scale Elastic Stack deployments, especially in sectors like finance, healthcare, and critical infrastructure, face higher operational risks.

To mitigate CVE-2026-26940, organizations should: 1) Monitor Elastic’s official channels for patches addressing this vulnerability and apply updates promptly once available. 2) Restrict access to the Timelion plugin to only trusted and necessary users by enforcing strict role-based access controls within Kibana. 3) Implement network segmentation and firewall rules to limit Kibana access to authorized personnel and systems. 4) Monitor Kibana logs for unusual or excessive Timelion expression submissions that may indicate exploitation attempts. 5) Consider disabling the Timelion plugin temporarily if it is not essential to reduce the attack surface. 6) Conduct regular audits of user accounts and permissions to minimize the risk of credential compromise. 7) Employ resource limits and monitoring on the Kibana host to detect and mitigate excessive memory usage early. These steps go beyond generic advice by focusing on access control, monitoring, and resource management specific to the Timelion plugin context.