CVE-2026-87012 in Open WebUI
Summary
by MITRE • 09/09/2026
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.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified in Open WebUI versions ranging from 0.9.0 to 0.11.1 represents a critical input validation failure within the backend calendar module, specifically located in the file open_webui/models/calendar.py. This flaw stems from the application's handling of the alert_minutes parameter associated with calendar events. When an authenticated user possessing calendar permissions creates or modifies an event, they can supply arbitrary data for this field without any server-side type checking to ensure it is a valid integer. The system accepts non-numeric values such as strings or special characters and stores them directly in the database alongside other event metadata. This lack of strict input validation allows malicious actors to inject malformed data that violates the expected schema for time-based calculations.
The operational impact of this vulnerability manifests during the execution of the shared upcoming-event scheduler, which runs periodically across the instance to evaluate pending reminders. The scheduling logic attempts to perform numerical comparisons between the current timestamp and the alert_minutes value stored in the database. Because the stored value is non-numeric, these arithmetic operations fail, triggering an unhandled exception within the Python runtime environment. This exception causes the entire scheduled task execution thread to abort immediately rather than skipping the single malformed record or logging a warning. Consequently, the instance-wide alert pass is terminated prematurely before it can process any remaining events in its queue.
This behavior results in a significant denial of service condition for all users relying on calendar reminders within the Open WebUI platform. Since the scheduler operates as an atomic batch process, the failure caused by one maliciously crafted event prevents the system from sending notifications to every other user whose alerts were scheduled to trigger during that cycle. The suppression persists until the next scheduled run or manual intervention occurs, effectively disabling a core functionality of the application for all tenants simultaneously. This constitutes a localized denial of service where a single authenticated action can degrade the availability and reliability of the platform's notification infrastructure without requiring elevated privileges or external network access.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the system fails to verify that user-supplied input conforms to expected data types before processing. It also relates to CWE-754 Improper Check for Unusual or Exceptional Conditions because the application does not gracefully handle unexpected data formats during critical arithmetic operations. In terms of attack vectors and tactics, this flaw can be leveraged within the MITRE ATT&CK framework under T1496 Resource Hijacking if used to consume system resources through repeated failures, though its primary impact is better described as a service disruption affecting availability rather than resource exhaustion in the traditional sense. It falls under the broader category of Availability impacts where an attacker disrupts normal operations by exploiting logic errors in scheduled tasks.
Mitigation strategies for this vulnerability involve both immediate patching and long-term architectural improvements. The most effective remediation is to upgrade Open WebUI to version 0.11.1 or later, where the developers have implemented proper type validation for the alert_minutes field. For environments that cannot immediately update, administrators should enforce strict input filtering at the API gateway level if possible, ensuring that only integer values are accepted by the calendar endpoints. Additionally, implementing robust error handling within the scheduler logic is recommended to prevent single-record failures from aborting entire batch processes. This can be achieved by wrapping individual event evaluations in try-catch blocks so that exceptions for specific records do not halt the execution of subsequent events. Regular security audits focusing on input validation and exception handling in scheduled background tasks will help identify similar weaknesses before they are exploited.