CVE-2026-45286: Nextcloud Calendar

Medium severity, CVSS 4.3. EPSS: 0.5% chance of exploitation in the next 30 days.

Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user can enumerate users on the same Nextcloud instance by using the Calendar app's endpoint for suggesting attendees. The sharing restrictions, applied to other endpoints, were not effective here. This issue has been patched in versions 5.5.17 and 6.2.3.

Affected products

• Nextcloud Calendar: from 5.5.13, before 5.5.17 (fixed in 5.5.17); from 6.2.0, before 6.2.3 (fixed in 6.2.3)

Published 2026-06-01. Last modified 2026-07-22.