CVE-2026-0543: Kibana Email Connector DoS Vulnerability

CVE-2026-0543 Overview

CVE-2026-0543 is an Improper Input Validation vulnerability (CWE-20) affecting Kibana's Email Connector functionality. The vulnerability allows an authenticated attacker with view-level privileges to cause an Excessive Allocation condition through a specially crafted email address parameter. When exploited, the application attempts to process the malformed email format, resulting in complete service unavailability for all users until a manual restart is performed.

Critical Impact

Authenticated attackers can cause complete Kibana service denial through crafted email address parameters, requiring manual intervention to restore availability.

Affected Products

• Kibana versions prior to 8.19.10
• Kibana versions prior to 9.1.10
• Kibana versions prior to 9.2.4

Discovery Timeline

• January 13, 2026 - CVE-2026-0543 published to NVD
• January 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-0543

Vulnerability Analysis

This vulnerability stems from insufficient input validation in Kibana's Email Connector component. When processing email address parameters, the application fails to properly validate the format and length of input data before attempting to process it. An attacker who has authenticated access with view-level privileges sufficient to execute connector actions can exploit this weakness.

The attack pattern aligns with CAPEC-130 (Excessive Allocation), where the attacker forces the system to allocate resources beyond what is necessary for normal operation. By submitting a specially crafted email address parameter to the Email Connector, the attacker can trigger a resource exhaustion condition that renders the entire Kibana service unavailable.

The requirement for authentication reduces the attack surface somewhat, but authenticated users with relatively low-privilege view-level access can still execute this attack. This makes the vulnerability particularly concerning in multi-tenant environments or organizations where many users have basic Kibana access.

Root Cause

The root cause of CVE-2026-0543 is improper input validation in the Email Connector's email address parameter handling. The application does not adequately sanitize or validate email address inputs before processing, allowing specially crafted values to trigger excessive memory or resource allocation. This lack of boundary checking enables an attacker to cause the application to enter a state where it consumes resources disproportionate to the input size.

Attack Vector

The attack is executed over the network by an authenticated user with view-level privileges. The attacker crafts a malicious email address parameter and submits it through the Email Connector action interface. Upon processing the malformed input, Kibana attempts to allocate excessive resources, leading to service degradation and ultimately complete unavailability. Recovery requires manual restart of the Kibana service.

The vulnerability mechanism involves the Email Connector's parameter parsing logic. When an attacker supplies a specially formatted email address value, the application's processing routine fails to impose appropriate limits on resource consumption. Technical details regarding the specific exploitation technique can be found in the Elastic Security Update ESA-2026-08.

Detection Methods for CVE-2026-0543

Indicators of Compromise

• Unusual memory consumption spikes in Kibana service processes
• Kibana service crashes or unresponsive states requiring manual restarts
• Abnormal connector action requests with malformed email address parameters in audit logs
• Error logs indicating resource exhaustion or allocation failures in the Email Connector

Detection Strategies

• Monitor Kibana service health metrics for sudden resource consumption increases or service unavailability
• Implement audit logging for connector action executions, particularly those involving the Email Connector
• Alert on repeated Kibana service restarts or crash events that may indicate ongoing exploitation attempts
• Review authentication logs to identify users executing connector actions with potentially malicious parameters

Monitoring Recommendations

• Configure alerting thresholds for Kibana memory and CPU utilization to detect resource exhaustion attacks early
• Enable verbose logging for connector actions to capture detailed parameter information for forensic analysis
• Implement service health checks with automatic alerting when Kibana becomes unresponsive
• Monitor network traffic for unusual patterns of requests to Kibana connector endpoints

How to Mitigate CVE-2026-0543

Immediate Actions Required

• Upgrade Kibana to version 8.19.10, 9.1.10, or 9.2.4 or later immediately to apply the security fix
• Review audit logs for any suspicious Email Connector activity that may indicate prior exploitation attempts
• Restrict connector action privileges to only users who require this functionality
• Implement network-level controls to limit access to Kibana connector endpoints where possible

Patch Information

Elastic has released security updates addressing this vulnerability. Patched versions include Kibana 8.19.10, 9.1.10, and 9.2.4. Organizations should update to one of these versions or later to remediate CVE-2026-0543. Full details are available in the Elastic Security Update ESA-2026-08.

Workarounds

• Temporarily disable or restrict access to the Email Connector feature if not critical to operations
• Limit connector action privileges to essential personnel only until patching is complete
• Implement application-layer firewall rules to filter requests containing malformed email parameters
• Configure resource limits and monitoring to detect and contain excessive allocation conditions

# Example: Restricting connector privileges via Kibana role configuration
# Navigate to Stack Management > Roles and modify connector permissions
# Ensure only necessary users have "Actions and Connectors: All" privileges
# Consider setting to "Actions and Connectors: Read" for non-administrative users