Bug 2483833 (CVE-2026-45281)

Summary: CVE-2026-45281 nextcloud-server: Nextcloud Server: Authenticated users can gain full calendar access due to improper authorization.
Product: [Other] Security Response Reporter: Jon Moroney <jmoroney>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Nextcloud Server. An authenticated user, with knowledge of another user's principal URL, could exploit improper authorization controls to gain full access to that user's calendar. This allows the attacker to view and modify the victim's calendar, leading to unauthorized information disclosure and data manipulation.
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Bug Depends On: 2483847, 2483848    
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Description Jon Moroney 2026-06-01 21:45:32 UTC
Nextcloud is an open source content collaboration platform. In Nextcloud Server from versions 32.0.0 to before 32.0.9, and 33.0.0 to before 33.0.3, with the knowledge of other users’ principal URL an attacker could possibly send a request to gain full access to their calendar. Therefore, the attacker must be an authenticated user. This is because of improper authorization controls in the backend of the calendar. If the attacker had access to the calendar, they would be able to view and modify it. It is recommended that the Nextcloud Server is upgraded to 33.0.3 or 32.0.9. It is recommended that the Nextcloud Enterprise Server is upgraded to 33.0.3, 32.0.9, 31.0.14.5, 30.0.17.9, 29.0.16.16, 28.0.14.17, 27.1.11.26, 26.0.13.26, 25.0.13.29, 24.0.12.34, 23.0.12.35, 22.2.10.39, or 21.0.9.23