Elk: Incorrect Authorization in Kibana Agent Builder Leading to Disclosure and Tampering of Private Agents (CVE-2026-72643)

Kibana Agent Builder uses a flawed authorization mechanism to verify ownership of private agents. When a stable user identifier is unavailable, it falls back to comparing usernames, which are not unique across different Elasticsearch authentication realms. This causes two distinct principals sharing the same username in separate realms to be treated as the same owner. Consequently, an attacker can view, alter, or remove private agents belonging to other users. The vulnerability affects Kibana versions >=9.4.0 <9.4.5 and >=9.5.0 <9.5.1. A patch is available to address this issue.

An attacker with a username that matches another user's username in a different Elasticsearch authentication realm can gain unauthorized access to private agent configurations and instructions. This enables disclosure of sensitive agent data and allows modification or removal of agents they do not own, potentially disrupting monitoring or management operations.

A patch is available for this vulnerability. Users should upgrade Kibana to versions 9.4.5 or later and 9.5.1 or later to remediate the issue. No additional mitigation steps are indicated by the vendor advisory.