# CVE-2026-109299: Open WebUI denial of service in recurrence rule validation

Source: https://junglewise.ai/threats/cve-2026-109299-open-webui-from-0-9-0-before-0-11-4-contains-a-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-12. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-109299 · Severity: medium · CVSS 6.5 · Published 2026-10-12

Open WebUI is a web interface for managing AI models and automations. Authenticated users with automations permission can cause the entire instance to become unresponsive by submitting specially crafted recurring event rules (like dates that never occur, such as February 30th) that consume seconds of processing time per request. An attacker could repeatedly send these malicious requests to effectively take the service offline for all users.

Technologies: [Open WebUI](https://junglewise.ai/threats/technologies/open-webui-open-webui). Vendors: [Open WebUI](https://junglewise.ai/threats/vendors/open-webui).

## Quick answers

**Is CVE-2026-109299 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-109299 being exploited in the wild.

**How severe is CVE-2026-109299?** Medium severity, with a CVSS score of 6.5, published 12 October 2026.

**Which products and versions are affected?** Open WebUI 0.9.0 to 0.11.3.

**Is there a fix for CVE-2026-109299?** Yes: fixed in 0.11.4. Until then: Restrict the automations feature (USER_PERMISSIONS_FEATURES_AUTOMATIONS) to trusted administrators only, or disable it entirely until 0.11.4 is deployed. Consider running multiple UVICORN_WORKERS to partially mitigate impact from a single blocked worker. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-109299 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-109299?** Check whether you run Open WebUI at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 0.11.4

Restrict the automations feature (USER_PERMISSIONS_FEATURES_AUTOMATIONS) to trusted administrators only, or disable it entirely until 0.11.4 is deployed. Consider running multiple UVICORN_WORKERS to partially mitigate impact from a single blocked worker.

## Technical details

The vulnerability exists in the recurrence rule validator in backend/open_webui/utils/automations.py. When validating RRULE strings for automations, the code calls the calendar library to find the next occurrence without time limits. Rules with impossible constraints (e.g., BYMONTHDAY=30 on February) cause the library to exhaust its entire search space before determining no match exists, blocking the async event loop synchronously for seconds per request. The POST /api/v1/automations/create and /api/v1/automations/{id}/update endpoints both invoke this validator directly, halting all concurrent request processing.

## Affected products

- Open WebUI Open WebUI 0.9.0 to 0.11.3

## Timeline

- 2026-09-27: disclosed
- 2026-09-21: patched: Fix committed in 5fb869d
- 2026-10-12: advisory

## References

- [https://github.com/open-webui/open-webui/commit/5fb869db221d9599a576e8e2eea9c3314947d25e](https://github.com/open-webui/open-webui/commit/5fb869db221d9599a576e8e2eea9c3314947d25e)
- [https://github.com/open-webui/open-webui/security/advisories/GHSA-5w58-mwmh-vf2m](https://github.com/open-webui/open-webui/security/advisories/GHSA-5w58-mwmh-vf2m)

## Related threats

- [Open WebUI stored cross-site scripting in Markdown renderer](https://junglewise.ai/threats/cve-2026-109300-open-webui-from-0-6-31-before-0-11-4-contains-a-stored-cross)
- [Open WebUI regex denial of service in file search tools](https://junglewise.ai/threats/cve-2026-109298-open-webui-0-11-0-before-0-11-4-compiles-user-chosen-grep)
- [Open WebUI automation recurrence-rule denial of service](https://junglewise.ai/threats/cve-2026-109297-open-webui-0-11-0-before-0-11-4-contains-a-denial-of-service)
- [Open WebUI missing authorization in model provider routes](https://junglewise.ai/threats/cve-2026-109296-open-webui-before-0-11-4-contains-a-missing-authorization)
- [Open WebUI regular expression denial of service in file search](https://junglewise.ai/threats/cve-2026-109295-open-webui-from-0-11-0-before-0-11-4-contains-a-regular)