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Vulnerability · Published Jun 1, 2026 · Assigned by GitHub_M

CVE-2026-45281Nextcloud: Cross-Account Calendar Takeover via Unauthorized Group-Member-Set Update

High 8.1

In plain English

A high-severity authorization bypass via user-controlled key in security-advisories from nextcloud. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities).

Severity (CVSS 3.1)8.1High
Exploit odds (30 days)0.3%top 79.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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

Affected products (as reported)

VendorProductVersions
nextcloud security-advisories >= 32.0.0, < 32.0.9>= 33.0.0, < 33.0.3

Weakness: CWE-639 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

References