CVE-2025-66511

4.8 MEDIUM
Published: December 05, 2025 Modified: December 10, 2025

Description

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for meeting proposals using a hash function, allowing an attacker to compute valid participant tokens, which allowed them to request details and submit dates in meeting proposals. The tokens are not purely random generated. This vulnerability is fixed in 6.0.3.

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CVSS v3.x Details

0.0 Low Medium High Critical 10.0
Vector String
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

References to Advisories, Solutions, and Tools

Patch Vendor Advisory Exploit Third Party Advisory
https://github.com/nextcloud/calendar/pull/7659
Source: security-advisories@github.com
Issue Tracking
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27
Source: security-advisories@github.com
Patch Vendor Advisory
https://hackerone.com/reports/3385434
Source: security-advisories@github.com
Permissions Required Vendor Advisory

4 reference(s) from NVD

Quick Stats

CVSS v3 Score
4.8 / 10.0
EPSS (Exploit Probability)
0.0%
5th percentile
Exploitation Status
Not in CISA KEV

Weaknesses (CWE)

Affected Vendors

nextcloud