Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.5",
  "pubDate": "2026-10-12T17:17:23.240Z",
  "pubdate": "2026-10-12T17:17:23.240Z",
  "executiveSummary": "Open WebUI versions 0.11.0 through 0.11.3 are susceptible to a Denial of Service (DoS) vulnerability within the automation recurrence-rule (RRULE) validator.\nThe vulnerability stems from a discrepancy between the strictness of the input validator and the underlying calendar library responsible for rule execution.\nAttackers with the authorization to create automations can craft malicious, whitespace-folded, or malformed RRULE strings that trigger high-frequency, synchronous expansion tasks.\nThis behavior forces the application's shared event loop to block for extended periods, causing severe service degradation or total unavailability.\nBecause the event loop is blocked on every scheduler poll, the denial of service is persistent and impacts all users of the platform.\nThe risk is categorized as high for multi-tenant environments where automation creation is a permitted user capability, as exploitation requires no special infrastructure beyond standard user access.",
  "technicalDetails": "The root cause of this vulnerability lies in an asynchronous mismatch between the input validation layer and the execution engine within the automation subsystem. Specifically, the recurrence-rule validator applies strict parsing logic to rule text, while the calendar library tasked with executing these rules utilizes a more lenient parsing mechanism.\nIn Open WebUI versions 0.11.0 to 0.11.3, an attacker can bypass the validator's intent by submitting malformed inputs—such as whitespace-folded rules, lowercase frequency identifiers, or missing RRULE prefixes—which the calendar library interprets as valid but highly intensive instructions.\nThe attack flow initiates when an authenticated user creates an automation containing a crafted RRULE string. Once the scheduler polls this rule, the calendar library expands the recurrence pattern per-second. Due to the nature of the event-loop architecture, this expansion occurs synchronously. The computation required to resolve these malicious rules effectively locks the event loop for several minutes per request.\nBecause the scheduler repeatedly processes these rules on every polling cycle, the application becomes caught in a loop of constant resource exhaustion. The synchronous blocking prevents the server from processing other concurrent requests, effectively stalling the event loop and causing a total denial of service for the product.\nThe vulnerability is restricted to authenticated users with the privilege to define automations. No further escalation is required to achieve the denial of service, as the payload is executed directly by the scheduler process. The impact is significant as it renders the application unresponsive, impacting both the user who created the automation and all other users on the shared instance."
}