CVE-2026-42397: Kibana DoS Vulnerability via Resource Allocation

CVE-2026-42397 Overview

CVE-2026-42397 is a denial of service vulnerability in Kibana caused by Allocation of Resources Without Limits or Throttling [CWE-770]. An authenticated user can submit a specially crafted request to affected Entity Analytics endpoints containing an oversized input value. The request triggers excessive resource consumption on the server, which may render Kibana unavailable to other users. Elastic addressed the issue in Kibana 9.3.7 and 9.4.4 through security update ESA-2026-55. The vulnerability requires low privileges and no user interaction, and it is exploitable over the network.

Critical Impact
Authenticated attackers can cause Kibana to become unavailable by sending oversized inputs to Entity Analytics endpoints, disrupting security monitoring and dashboards for all users.

Affected Products

Kibana versions prior to 9.3.7
Kibana 9.4.x versions prior to 9.4.4
Elastic Stack deployments exposing Entity Analytics endpoints

Discovery Timeline

2026-07-21 - CVE-2026-42397 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-42397

Vulnerability Analysis

The vulnerability resides in Kibana's Entity Analytics endpoints, which accept user-supplied input without enforcing size or resource limits. When a client submits a request containing an oversized input value, the server allocates memory and CPU proportional to that input. The absence of throttling or bounds checking allows a single authenticated user to exhaust available resources. Repeated or sufficiently large requests can prevent Kibana from servicing legitimate requests, resulting in a denial of service condition for the entire instance.

Root Cause

The root cause is a missing input size limit on request parameters processed by Entity Analytics endpoints. The affected code paths do not validate or cap the size of incoming values before allocating buffers, parsing structures, or performing analytics calculations. This design flaw maps to CWE-770, Allocation of Resources Without Limits or Throttling, and enables the Excessive Allocation attack pattern described in CAPEC-130.

Attack Vector

Exploitation requires network access to a Kibana instance and valid authentication with at least low-level privileges. No user interaction is required. An attacker submits a crafted HTTP request to an affected Entity Analytics endpoint, populating a target field with an oversized value. The server processes the input, allocates disproportionate memory or CPU, and becomes unresponsive. Because the vulnerability affects availability only, confidentiality and integrity of data remain intact. Full exploitation details have not been published. Refer to the Elastic Security Update ESA-2026-55 for vendor-supplied technical context.

Detection Methods for CVE-2026-42397

Indicators of Compromise

Unusually large request bodies or query parameters sent to Kibana Entity Analytics endpoints
Sudden spikes in Kibana Node.js process memory or CPU usage without a corresponding increase in user activity
Repeated HTTP 5xx responses or timeouts from Kibana following requests from a single authenticated account
Kibana process restarts or out-of-memory kills in system logs

Detection Strategies

Inspect Kibana access logs for requests targeting Entity Analytics routes with abnormally large payload sizes.
Correlate authenticated user activity with resource utilization spikes on Kibana hosts to identify abusive sessions.
Alert on Kibana health check failures or repeated readiness probe timeouts in orchestrated environments.

Monitoring Recommendations

Ingest Kibana and reverse proxy logs into a centralized analytics platform such as Singularity Data Lake for retention and correlation.
Establish baselines for request size distribution on Entity Analytics endpoints and alert on deviations.
Monitor per-user request rates and payload sizes to identify authenticated accounts issuing anomalous traffic.

How to Mitigate CVE-2026-42397

Immediate Actions Required

Upgrade Kibana to version 9.3.7, 9.4.4, or later as documented in ESA-2026-55.
Audit accounts with access to Entity Analytics features and remove unnecessary privileges.
Review recent authentication logs for suspicious sessions that may have probed affected endpoints.

Patch Information

Elastic released fixed versions Kibana 9.3.7 and 9.4.4 under advisory ESA-2026-55. The patches introduce input size validation on Entity Analytics endpoints. Full release notes and upgrade guidance are available in the Elastic Security Update ESA-2026-55.

Workarounds

Restrict network access to Kibana so that only trusted users can reach Entity Analytics endpoints.
Enforce request size limits at an upstream reverse proxy or web application firewall in front of Kibana.
Revoke Entity Analytics privileges from roles that do not require them until the patch is applied.

bash

# Example NGINX reverse proxy limit to cap request body size in front of Kibana
server {
    listen 443 ssl;
    server_name kibana.example.com;

    client_max_body_size 1m;

    location / {
        proxy_pass http://kibana_upstream;
        proxy_set_header Host $host;
        proxy_read_timeout 30s;
    }
}