An authentication-based flaw in Open WebUI 0.9.0 through 0.11.3 allows an attacker with automations permission to submit unsatisfiable recurrence rules—such as February 30th—into the automation create or update endpoints. The server processes these malformed rules, causing the shared event loop to stall for several seconds per request. Each improper rule execution reloads the loop, effectively denying service to all users until the loop clears the backlog.

The vulnerability affects the Open WebUI product with version numbers prior to 0.11.4, specifically the releases built from 0.9.0 up to 0.11.3 inclusive. The affected portfolio is identified as open-webui:open-webui, covering all distributions of the WebUI application that include the automations feature.

The CVSS score of 7.1 signals a high severity impact, while the EPSS score of <1% indicates a low exploitation probability at this time. The vulnerability is not cataloged in the CISA Known Exploited Vulnerabilities list, suggesting no confirmed active exploitation. Attackers must be authenticated and possess automations permission, limiting the attack surface to users who can create or edit automated tasks. When leveraged, each request can temporarily block the shared event loop, producing noticeable downtime for all users on the instance.