CVE-2026-54006: Open WebUI Calendar Authorization Bypass – Patch Guidance

Technical summary

CVE-2026-54006 exists in the POST /api/v1/calendars/events/{event_id}/update endpoint in Open WebUI prior to version 0.9.6. The endpoint performs authorization validation on the source calendar (confirming the caller can write to the calendar where the event currently resides) but fails to validate the destination calendar_id parameter supplied in the request body. The model layer then unconditionally persists the new calendar_id without re-checking authorization. This violates the principle of least privilege and mirrors a different authorization check that is correctly implemented in the create_event operation. The vulnerability is classified as CWE-639 (Authorization Bypass Through User-Controlled Key).

Business impact

The vulnerability enables data exposure and potential data manipulation within multi-tenant or multi-user Open WebUI deployments. An attacker with a regular user account can move sensitive calendar events (which may contain meeting notes, schedules, or confidential information) into calendars they control for inspection, or move events into calendars belonging to other users as a form of disruption or impersonation. In environments where calendar events are tied to workflow automation or scheduling of critical tasks, this could result in operational confusion or sabotage. The impact is limited by the fact that the attacker must know the target calendar ID and requires valid authentication to the platform.

Affected systems

Open WebUI versions prior to 0.9.6 are affected. This includes all deployments running 0.9.5 and earlier. The vulnerability affects any Open WebUI instance configured for multi-user access where users have different calendars. Self-hosted deployments are the primary target since Open WebUI is designed to operate offline; air-gapped or internal instances are equally vulnerable if multiple users share the platform.

Exploitability

The vulnerability has low barrier to exploitation. An attacker needs only a valid user account (not admin or elevated privileges) and network access to the Open WebUI API endpoint. No user interaction is required, and exploitation can be fully automated. The attacker must know or enumerate the calendar_id of the target calendar, which may be discoverable through the same API or via observation of shared calendar references. No complex attack chain is necessary. The CVSS 3.1 score of 4.3 (Medium) reflects the requirement for prior authentication and the limitation that integrity is affected but confidentiality and availability are not directly compromised at the system level.

Remediation

Upgrade Open WebUI to version 0.9.6 or later. This patch adds authorization validation to the calendar event update endpoint, ensuring that any attempt to move an event to a different calendar is checked against the user's write permissions on the destination calendar. For organizations unable to upgrade immediately, consider restricting API access to the /api/v1/calendars/events endpoint via network-level controls or Web Application Firewall rules, or implementing application-level role-based access controls that override the default behavior until a patch is applied.

Patch guidance

Organizations should prioritize upgrading to Open WebUI 0.9.6 as part of their routine patch management process. Since the vulnerability requires user authentication and affects only calendar features, it may be lower priority than critical vulnerabilities but should not be deferred indefinitely in multi-user deployments. Test the upgrade in a staging environment first to ensure compatibility with existing calendar integrations or customizations. The patch is relatively low-risk as it adds a missing authorization check without removing functionality.

Detection guidance

Monitor API logs for repeated POST requests to /api/v1/calendars/events/{event_id}/update endpoints where the calendar_id in the request body differs from the calendar_id of the event's current parent, especially from the same user account in rapid succession or targeting multiple distinct calendar IDs. Anomalous calendar ownership changes (events appearing in calendars they should not belong to) may also indicate exploitation. Implement API request logging that captures the full request body for audit review. Consider configuring alerts if a single user account moves events to an unusual number of different calendars in a short time window.

Why prioritize this

This vulnerability merits prompt patching but is not an immediate emergency. It requires authentication and does not directly impact system confidentiality or availability. However, in organizations where calendar data is sensitive, or where Open WebUI is used in a multi-user environment where users do not implicitly trust each other, the integrity impact warrants timely remediation. The low CVSS score should not be mistaken for low business risk in specific contexts.

Risk score, explained

The CVSS 3.1 score of 4.3 (Medium) reflects: (1) network-accessible API requiring only low-privilege user authentication (PR:L); (2) no special attack complexity beyond crafting a valid API request (AC:L); (3) integrity impact limited to the ability to move events between calendars (I:L); and (4) no direct impact on confidentiality or system availability (C:N/A:N). The score does not account for business-context factors such as the sensitivity of calendar data in a given organization, which may elevate actual risk.

Frequently asked questions