CVE-2026-45281 Nextcloud: Cross-Account Calendar Takeover via Unauthorized Group-Member-Set Update
Authenticated attackers can access and modify other users' calendars by exploiting improper authorization checks in the backend.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45281?
CVE-2026-45281 is a high-severity missing authorization vulnerability in Nextcloud Nextcloud Server, published on 1 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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
Weakness: CWE-639
Which versions are affected by CVE-2026-45281?
1 open source package ship an affected version, including nextcloud. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nextcloud Bitnami | From 32.0.0 | 32.0.9, 33.0.3 |
Products include Nextcloud Nextcloud Server.
How do I fix CVE-2026-45281?
Upgrade nextcloud to a fixed version for your release line: 32.0.9 or 33.0.3.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-45281 being exploited?
There is no known exploitation of CVE-2026-45281 in the wild and no public exploit code.
Other vulnerabilities in Nextcloud Nextcloud Server
- CVE-2021-32802 Preview generation used third-party library not suited for user-generated content in Nextcloud server
- CVE-2023-26482 Scope of workflow operations is not validated in nextcloud server
- CVE-2018-3775 Auth bypass in Nextcloud Server
- CVE-2023-35172 Nextcloud Server password reset endpoint is not brute force protected
- CVE-2023-32320 Nextcloud Server's brute force protection allows someone to send more requests than intended
Sources
Also known as BIT-nextcloud-2026-45281, GHSA-hrrv-mp25-26vv.