CVE-2026-45281 [High] | Security Vulnerability in Nextcloud Server

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

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.03%	0.28%	+0.25%
2	2026-06-02	—	0.03%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.03%

0.28%

+0.25%

2026-06-02

—

0.03%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
8.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	2.8	5.2	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

8.1

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

2.8

5.2

[email protected]

Affected software / configurations for CVE-2026-45281

Vendor	Product	Version	Raw CPE
nextcloud	nextcloud_server	>= 32.0.0, < 32.0.9	cpe:2.3:a:nextcloud:nextcloud_server:::::-:::*
nextcloud	nextcloud_server	>= 33.0.0, < 33.0.3	cpe:2.3:a:nextcloud:nextcloud_server:::::-:::*
nextcloud	nextcloud_server	>= 21.0.0, < 21.0.9.23	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 22.0.0, < 22.2.10.39	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 23.0.0, < 23.0.12.35	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 24.0.0, < 24.0.12.34	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 25.0.0, < 25.0.13.29	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 26.0.0, < 26.0.13.26	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 27.0.0, < 27.1.11.26	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 28.0.0, < 28.0.14.17	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 29.0.0, < 29.0.16.16	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 30.0.0, < 30.0.17.9	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 31.0.0, < 31.0.14.5	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 32.0.0, < 32.0.9	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*
nextcloud	nextcloud_server	>= 33.0.0, < 33.0.3	cpe:2.3:a:nextcloud:nextcloud_server:::::enterprise:::*

References for CVE-2026-45281

URL	Tags
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-hrrv-mp25-26vv	Mitigation Vendor Advisory
https://github.com/nextcloud/server/pull/59962	Issue Tracking Patch
https://hackerone.com/reports/3545964	Permissions Required

URL

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

Exploit prediction scoring system (EPSS) score for CVE-2026-45281

Common vulnerability scoring system (CVSS) metrics for CVE-2026-45281

Weakness enumeration for CVE-2026-45281

Affected software / configurations for CVE-2026-45281

References for CVE-2026-45281