CVE-2026-26936: 
Kibana vulnerability analysis and mitigation

CVE-2026-26936 is a ReDoS (Regular Expression Denial of Service) vulnerability caused by Inefficient Regular Expression Complexity (CWE-1333) in the AI Inference Anonymization Engine of Kibana. It allows an authenticated attacker with high privileges to trigger a Denial of Service condition via Regular Expression Exponential Blowup (CAPEC-492). Affected versions include Kibana 8.0.0 through 8.19.10 and 9.0.0 through 9.2.4. The vulnerability was published on February 26, 2026, with patches released in Kibana 8.19.11 and 9.2.5. It carries a CVSS v3.1 base score of 7.5 (High) per NVD, though ENISA's EUVD rates it 4.9 (Medium) reflecting the high-privilege requirement (Elastic Advisory, Red Hat).

The root cause is CWE-1333 (Inefficient Regular Expression Complexity) within Kibana's AI Inference Anonymization Engine, where one or more regular expressions are susceptible to exponential backtracking when evaluated against specially crafted input strings. This attack pattern is classified as CAPEC-492 (Regular Expression Exponential Blowup), commonly known as ReDoS. An attacker with high administrative privileges can submit a crafted request containing a malicious input string that causes the regex engine to enter catastrophic backtracking, consuming excessive CPU resources. No public proof-of-concept exploit code has been identified at this time (Elastic Advisory, Red Hat).

Successful exploitation causes the Kibana AI Inference Anonymization Engine to consume excessive CPU resources, resulting in service unavailability (Denial of Service) for all legitimate users of the affected Kibana instance. There is no confidentiality or integrity impact — the vulnerability is limited to availability. Because exploitation requires high privileges, the blast radius is constrained, but a malicious insider or compromised privileged account could disrupt Kibana operations for an entire organization relying on the platform for observability or security analytics (Elastic Advisory).

There is no known public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of publication. The EPSS score is approximately 0.036%, indicating a very low probability of exploitation in the near term. Exploitation requires network access and authenticated high-privilege credentials, significantly limiting the attacker pool. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog (Elastic Advisory, Red Hat).

1. Reconnaissance: Identify a Kibana instance running a vulnerable version (8.0.0–8.19.10 or 9.0.0–9.2.4) with the AI Inference Anonymization Engine enabled.
2. Authentication: Authenticate to Kibana using a high-privilege account (e.g., administrator or superuser role).
3. Craft malicious input: Construct a specially crafted string designed to trigger catastrophic backtracking in the vulnerable regular expression(s) used by the AI Inference Anonymization Engine — typically a string with repetitive patterns that cause exponential evaluation paths.
4. Submit request: Send the crafted input via the relevant Kibana API endpoint or UI feature that invokes the AI Inference Anonymization Engine.
5. Trigger DoS: The regex engine enters exponential backtracking, consuming all available CPU resources on the Kibana server, causing the service to become unresponsive or crash for all users (Elastic Advisory).

• Logs: Kibana server logs showing repeated or long-running requests to AI Inference Anonymization Engine endpoints; timeout or unresponsive errors in Kibana application logs.
• System Metrics: Sudden spike in CPU utilization on the Kibana host process (Node.js) to near 100%, sustained over an extended period without a corresponding increase in legitimate user activity.
• Network: Unusual or repeated API calls from a privileged account to AI inference-related Kibana endpoints, particularly with atypical or oversized input payloads.
• Availability: Kibana health checks failing or the service becoming unresponsive, coinciding with the above CPU anomalies (Elastic Advisory).

Elastic has released patched versions: Kibana 8.19.11 (for the 8.x branch) and Kibana 9.2.5 (for the 9.x branch). Organizations should upgrade to these versions as the primary remediation. As a compensating control, restrict administrative access to Kibana to only necessary personnel, reducing the pool of accounts that could trigger exploitation. Additionally, monitor Kibana availability and CPU utilization for anomalous spikes that may indicate a DoS attempt (Elastic Advisory).

The vulnerability received standard coverage across vulnerability tracking platforms and security community feeds shortly after disclosure. A technical deep-dive was published by Undercode Testing, framing the issue as a ReDoS risk to Kibana clusters (Undercode Testing). NetEye also referenced the vulnerability in a broader Elastic Stack security advisory (NetEye Blog). Community reaction was measured, reflecting the limited exploitability due to the high-privilege requirement.