CVE-2026-109297 in Open WebUI
Summary
by MITRE • 10/12/2026
Open WebUI 0.11.0 before 0.11.4 contains a denial of service vulnerability in the automation recurrence-rule validator, whose sub-daily frequency guard parses rule text more strictly than the calendar library that executes it. Users permitted to create automations can submit whitespace-folded rules (or, in 0.11.0, lowercase frequencies or omitted RRULE prefixes) that expand per-second synchronously, blocking the shared event loop for minutes per request and on every scheduler poll.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in Open WebUI versions prior to 0.11.4 represents a significant denial of service risk rooted in input validation inconsistencies within the automation recurrence-rule validator. This flaw specifically affects how sub-daily frequency rules are processed, creating a discrepancy between the parsing logic used for validation and the execution engine provided by underlying calendar libraries. The core technical issue arises because the application's internal parser enforces stricter formatting requirements than the actual library responsible for calculating recurring events. Consequently, inputs that would normally be rejected as malformed or invalid due to minor syntactic deviations are inadvertently accepted during the initial validation phase but trigger catastrophic behavior when passed to the execution engine.
Specifically, users with permissions to create automations can exploit this discrepancy by submitting whitespace-folded rules, which involve removing spaces from standard rule definitions. In version 0.11.0 of Open WebUI, additional vectors exist where lowercase frequency indicators or omitted RRULE prefixes are accepted despite being non-standard. When these malformed inputs reach the scheduler, they cause the calendar library to interpret them as high-frequency events that expand synchronously on a per-second basis. This results in an infinite loop-like behavior within the application's main thread, effectively blocking the shared event loop for extended periods, often lasting several minutes per request.
The operational impact of this vulnerability is severe due to its potential for resource exhaustion and service disruption. Because Open WebUI relies on a single-threaded or limited-concurrency model for handling scheduler polls, a single maliciously crafted automation rule can monopolize the processing capacity of the server. This blocks all other concurrent operations, including user interface interactions, API requests, and background tasks, leading to a complete unavailability of the service for legitimate users. The attack does not require authentication bypass or complex exploitation techniques; it merely requires that an attacker possess basic permissions to create automations within the system, which is often granted to standard users in collaborative environments.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-400 Uncontrolled Resource Consumption. The failure lies in the application's inability to normalize or strictly validate input against the actual capabilities of its dependencies before execution. Furthermore, from an offensive security standpoint such as MITRE ATT&CK, this behavior facilitates Denial of Service via resource exhaustion (T1496) and potentially impacts Availability by disrupting critical business processes through automated task manipulation.
Mitigation strategies must prioritize immediate patching to version 0.11.4 or later, where the parsing logic has been aligned with the execution library's expectations. In environments where upgrading is not immediately feasible, administrators should restrict automation creation privileges to trusted administrative accounts only. Additionally, implementing rate limiting on API endpoints related to automation management can help mitigate the impact by preventing rapid successive requests that could compound the resource exhaustion effect. Input sanitization layers at the network perimeter may also filter out suspiciously formatted recurrence rules before they reach the application logic, although this is a secondary defense compared to fixing the root cause in the codebase.