Description

Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.9.0 until 0.11.1, backend/open_webui/models/calendar.py stored the calendar event meta.alert_minutes value without type validation and the shared upcoming-event scheduler compared that value numerically. An authenticated user with the calendar permission could store a non-numeric alert_minutes value that raised an exception and aborted the instance-wide alert pass, suppressing all users' reminders while the event remained in the lookahead window. This issue is fixed in version 0.11.1.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-09-09T21:17:06.030Z",
  "pubdate": "2026-09-09T21:17:06.030Z",
  "executiveSummary": "This vulnerability is an improper input validation flaw identified in Open WebUI versions 0.9.0 through 0.11.1, resulting in a Denial-of-Service (DoS) condition for the calendar notification system.\nThe issue stems from the lack of type validation for the 'alert_minutes' field within the calendar event metadata, specifically in 'backend/open_webui/models/calendar.py'.\nAn authenticated user possessing standard calendar permissions can inject non-numeric data into the 'alert_minutes' parameter. When the backend scheduler processes upcoming events, it attempts a numeric comparison against this unvalidated input, triggering an unhandled exception.\nThis exception terminates the instance-wide alert execution pass, effectively suppressing all calendar reminders for every user on the platform as long as the malicious event remains within the system's lookahead window.\nThe vulnerability represents a significant service availability risk, as it allows a single authenticated user to disable global notification functionality without requiring administrative privileges. Exploitation is trivial, requiring only the ability to create or modify a calendar event. Mitigation is achieved by upgrading to version 0.11.1 or later, where input sanitization and type enforcement have been implemented.",
  "technicalDetails": "The vulnerability is located in 'backend/open_webui/models/calendar.py', where the application handles the storage and retrieval of calendar event metadata. The system allows users with calendar permissions to define an 'alert_minutes' value, which determines the lead time for event reminders.\nThe root cause is a failure to enforce strict type checking or sanitization on the 'alert_minutes' field before the data is persisted. The backend implementation assumes that the stored value will always be of an integer type suitable for arithmetic comparison.\nThe attack flow proceeds as follows: First, an authenticated attacker crafts a calendar event via the application's interface or API, setting the 'alert_minutes' metadata field to a non-numeric string or an incompatible data type. Because the backend fails to perform server-side validation during the save operation, the malicious metadata is committed to the underlying database.\nThe platform utilizes an automated, instance-wide scheduler that periodically iterates through upcoming events to evaluate whether a notification needs to be dispatched. During this 'alert pass,' the application logic retrieves the 'alert_minutes' value and performs a mathematical operation (numeric comparison) against the current time delta.\nWhen the scheduler encounters the non-numeric value injected by the attacker, the Python runtime raises a 'TypeError' (or similar exception depending on the comparison logic), which is not caught within the scheduler's loop. This unhandled exception causes the immediate termination of the entire execution thread responsible for the alert pass.\nConsequently, the scheduler fails to process any subsequent events in the queue for the current lookahead window. As long as the malformed event exists in the database and falls within the lookahead parameters, every subsequent execution of the scheduler will encounter the same exception and crash, resulting in a persistent Denial-of-Service for the notification system across the entire instance.\nThis vulnerability affects Open WebUI versions 0.9.0 through 0.11.1. It requires an authenticated user with existing calendar permissions, but does not require administrative access. The impact is limited to the functionality of the calendar alert system; it does not lead to remote code execution or unauthorized data access, but it effectively cripples the platform's ability to provide timely event reminders to the user base."
}