CVE-2026-42399: Kibana Denial of Service via Timelion Expression Overflow

Technical summary

CVE-2026-42399 is an uncontrolled resource consumption vulnerability (CWE-400) affecting Elastic Kibana. The vulnerability exists in the Timelion visualization engine, which fails to properly bound memory allocation when processing expressions containing excessive levels of chained function calls. An authenticated user can craft a malicious visualization expression that generates a data structure of exponential size. The unchecked recursion or nesting causes the Kibana process to exhaust available heap memory, triggering an out-of-memory condition and service crash. The attack vector is network-accessible, requires low-privilege authentication, and does not require user interaction to execute.

Business impact

Successful exploitation results in denial of service affecting all Kibana users in an affected environment. Analytics, log analysis, and dashboard visibility are unavailable until the service is manually restarted. For organizations using Kibana for security operations, real-time visibility into events is lost during the outage, creating potential blind spots for threat detection. Recovery requires manual intervention, potentially extending downtime. The attack surface includes any authenticated user—including service accounts with minimal privileges—reducing the barrier to exploitation.

Affected systems

Elastic Kibana is affected. The vulnerability is specific to the Timelion visualization feature. Organizations running Kibana as part of the Elastic Stack (formerly ELK Stack) are at risk. Verify the specific affected version range against the Elastic security advisory, as the source data does not specify version boundaries.

Exploitability

Exploitability is moderate. The attack requires valid authentication credentials, which constrains the attack to insider threats or accounts obtained through credential compromise. No user interaction is required once the crafted visualization is submitted. The low barrier to execution—simply uploading a visualization—means that any authenticated user, regardless of privilege level, can trigger the denial of service. Public exploit code has not been identified in known exploit databases as of the advisory date.

Remediation

Apply the security patch provided by Elastic for Kibana. Organizations should prioritize patching based on their exposure to untrusted users with Kibana access. As an interim mitigation, restrict Timelion visualization creation and editing to trusted users, or disable Timelion entirely if not required. Monitor Kibana process memory usage and implement automatic alerting if memory consumption spikes unexpectedly.

Patch guidance

Refer to the official Elastic security advisory for the specific patched version that addresses CVE-2026-42399. Patches are typically released for active maintenance branches; verify your version against the advisory to identify the upgrade path. Test patches in a non-production environment before deploying to production Kibana clusters. Patching may require a service restart depending on your Kibana deployment model.

Detection guidance

Monitor Kibana process memory consumption for unexplained spikes, particularly after visualization creation or modification events. Log authentication events combined with Timelion visualization submissions from unusual or lower-privileged accounts. Implement alerting on Kibana service crashes or out-of-memory errors. If possible, instrument Timelion expression parsing to detect pathologically nested or deeply chained function calls before execution.

Why prioritize this

This vulnerability merits prompt attention despite its MEDIUM CVSS score because it enables any authenticated user to disrupt critical analytics infrastructure. The low barrier to exploitation and high operational impact make it a priority for environments where Kibana availability is essential to security operations or business intelligence workflows. Insider threat and credential compromise scenarios elevate risk.

Risk score, explained

The CVSS 3.1 score of 6.5 (MEDIUM) reflects the requirement for authentication (PR:L) and the lack of confidentiality or integrity impact (C:N/I:N). The score emphasizes availability impact (A:H), recognizing that complete denial of service is possible. The network-accessible vector (AV:N) and low attack complexity (AC:L) increase the score relative to a purely local vulnerability. Organizations dependent on Kibana for operational visibility may consider this functionally higher-risk than the base CVSS suggests.

Frequently asked questions