CVE-2026-26940: Kibana Timelion Plugin DoS Vulnerability

CVE-2026-26940 Overview

CVE-2026-26940 is an Improper Validation of Specified Quantity in Input vulnerability (CWE-1284) affecting the Timelion visualization plugin in Kibana. This vulnerability allows an authenticated user to send a specially crafted Timelion expression that overwrites internal series data properties with an excessively large quantity value, leading to Denial of Service via Excessive Allocation (CAPEC-130).

Critical Impact

Authenticated attackers can cause resource exhaustion and service unavailability by exploiting improper input validation in Timelion expressions.

Affected Products

• Kibana versions prior to 8.19.13
• Kibana versions prior to 9.2.7
• Kibana versions prior to 9.3.2

Discovery Timeline

• 2026-03-19 - CVE CVE-2026-26940 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-26940

Vulnerability Analysis

This vulnerability stems from insufficient validation of user-supplied quantity values within the Timelion visualization plugin. The Timelion plugin processes time-series expressions that allow users to manipulate and visualize data. When processing these expressions, the plugin fails to properly validate numeric quantities specified by users, allowing attackers to inject excessively large values that overwhelm system resources.

The attack requires authentication, meaning only users with valid Kibana credentials can exploit this vulnerability. However, once authenticated, an attacker can craft malicious Timelion expressions that cause the server to allocate excessive amounts of memory, potentially rendering the Kibana service unavailable to legitimate users.

Root Cause

The root cause is improper validation of specified quantity in input (CWE-1284). The Timelion plugin does not enforce appropriate bounds checking on numeric values provided within Timelion expressions. This allows attackers to specify arbitrarily large quantities that, when processed, trigger excessive memory allocation operations. The lack of input sanitization permits internal series data properties to be overwritten with malicious values.

Attack Vector

The attack is network-accessible and requires low privilege (authenticated user). An attacker with valid Kibana credentials can submit specially crafted Timelion expressions through the web interface. The malicious expression contains excessively large quantity values that, when parsed and processed by the Timelion plugin, cause the server to attempt allocating more memory than available resources can support.

The vulnerability exploits the Excessive Allocation pattern (CAPEC-130), where the attacker forces the application to allocate resources in quantities that exceed reasonable limits, ultimately exhausting available system memory and causing service degradation or complete denial of service.

Detection Methods for CVE-2026-26940

Indicators of Compromise

• Unusual memory consumption spikes on Kibana server processes
• Timelion queries containing abnormally large numeric values in expressions
• Repeated Kibana service crashes or restarts due to out-of-memory conditions
• Error logs indicating memory allocation failures in Timelion plugin operations

Detection Strategies

• Monitor Kibana application logs for unusual Timelion expression patterns or parsing errors
• Implement anomaly detection for memory usage on Kibana server instances
• Review audit logs for repeated Timelion queries from the same authenticated user
• Alert on Kibana process memory consumption exceeding baseline thresholds

Monitoring Recommendations

• Configure resource usage alerts for Kibana containers or virtual machines
• Implement query logging and analysis for Timelion visualization requests
• Deploy application performance monitoring (APM) to track Timelion plugin behavior
• Establish baseline metrics for normal Timelion query resource consumption

How to Mitigate CVE-2026-26940

Immediate Actions Required

• Upgrade Kibana to version 8.19.13, 9.2.7, or 9.3.2 or later immediately
• Review Kibana access controls and ensure only authorized users have access to Timelion functionality
• Consider temporarily disabling the Timelion plugin if patching is delayed
• Monitor system resources for signs of active exploitation

Patch Information

Elastic has released security updates addressing this vulnerability. Refer to the Elastic Security Update (ESA-2026-20) for detailed patching instructions and version-specific guidance. Organizations should prioritize upgrading to the patched versions: 8.19.13, 9.2.7, or 9.3.2.

Workarounds

• Restrict access to Kibana and the Timelion plugin to trusted users only
• Implement network-level access controls to limit who can reach the Kibana interface
• Configure resource limits (memory, CPU) for Kibana processes to contain potential impact
• Disable the Timelion visualization plugin if it is not required for operations

# Example: Configure Kibana memory limits in systemd service file
# /etc/systemd/system/kibana.service.d/override.conf
[Service]
MemoryLimit=4G
MemoryMax=4G