Executive Summary

CVE-2026-0817 is an authorization vulnerability in the Wikimedia Foundation's MediaWiki CampaignEvents extension. Specifically, the API endpoint GET campaignevents/v0/event_registration/{id} exposed sensitive meeting and chat URLs without proper authorization checks. While the user interface restricted these URLs to registered participants, the API allowed any requester to access them, leading to unauthorized disclosure of sensitive event information. The issue was temporarily mitigated by removing these fields from the API response, with a permanent fix planned to enforce proper permission checks. [1]

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Impact Analysis

This vulnerability can lead to unauthorized access to sensitive meeting and chat URLs of events managed through the CampaignEvents extension. An attacker or unauthorized user could obtain these URLs without permission, potentially allowing them to join private meetings or chats, leading to privacy breaches or misuse of event communications. However, the risk was considered low due to limited third-party usage of the extension and the immediate deployment of a temporary patch. [1]

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Detection Guidance

Detection of this vulnerability involves checking if the CampaignEvents extension's API endpoint GET campaignevents/v0/event_registration/{id} is accessible without authorization and if it returns meeting and chat URLs. You can test this by sending an unauthenticated HTTP GET request to the endpoint and inspecting the response for sensitive URLs. For example, using curl: curl -X GET https://your-mediawiki-site/api/rest_v1/campaignevents/v0/event_registration/{id} -i. If the response includes meeting or chat URLs without requiring authentication, the system is vulnerable. [1]

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Mitigation Strategies

The immediate mitigation step is to deploy the temporary patch that removes the meeting and chat URL fields from the API response entirely, preventing unauthorized disclosure. This quick fix was applied in Wikimedia production to block sensitive data exposure while a more comprehensive permission enforcement patch was developed. Applying this temporary patch or upgrading to a version that includes it is recommended as an immediate action. [1]

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