CVE-2026-45281

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

HIGH

8.1

CVSS Score

Published: June 1, 2026 at 04:52 PM UTC

Updated: July 22, 2026 at 07:37 AM UTC

1 product affected across 1 vendorNextcloud/server

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Severity

HIGH8.1

Exploit prediction

EPSS 0.3%

SSVC

No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Nextcloud/server · Nextcloudnextcloud-app

95%

21.0.0 ≤ v < 21.0.9.2322.0.0 ≤ v < 22.2.10.3923.0.0 ≤ v < 23.0.12.3524.0.0 ≤ v < 24.0.12.3425.0.0 ≤ v < 25.0.13.2926.0.0 ≤ v < 26.0.13.2627.0.0 ≤ v < 27.1.11.2628.0.0 ≤ v < 28.0.14.1729.0.0 ≤ v < 29.0.16.1630.0.0 ≤ v < 30.0.17.931.0.0 ≤ v < 31.0.14.532.0.0 ≤ v < 32.0.933.0.0 ≤ v < 33.0.3

Affected range stops below 21.0.9.23, so it looks safe — our inference, not a vendor statement

Affected range stops below 22.2.10.39, so it looks safe — our inference, not a vendor statement

Affected range stops below 23.0.12.35, so it looks safe — our inference, not a vendor statement

Affected range stops below 24.0.12.34, so it looks safe — our inference, not a vendor statement

Affected range stops below 25.0.13.29, so it looks safe — our inference, not a vendor statement

Affected range stops below 26.0.13.26, so it looks safe — our inference, not a vendor statement

Affected range stops below 27.1.11.26, so it looks safe — our inference, not a vendor statement

Affected range stops below 28.0.14.17, so it looks safe — our inference, not a vendor statement

Affected range stops below 29.0.16.16, so it looks safe — our inference, not a vendor statement

Affected range stops below 30.0.17.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 31.0.14.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 32.0.9, so it looks safe — our inference, not a vendor statement

Affected range stops below 33.0.3, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (3)

x_refsource_CONFIRMMitigationVendor Advisory

Source: cverecord

https://github.com/nextcloud/security-advisories/security/advisories/GHSA-hrrv-mp25-26vv

x_refsource_MISCIssue TrackingPatch

Source: cverecord

https://github.com/nextcloud/server/pull/59962

x_refsource_MISCPermissions Required

Source: cverecord

https://hackerone.com/reports/3545964

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.1HIGHGitHub_M

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: HIGH
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-639

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