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3.3
LOW CVSS 3.1
CVE-2025-66546
Nextcloud Calendar app allowed booking appointments without the generated token
Description

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.19, 5.5.6, and 6.0.1, the calendar app allowed blindly booking appointments with a squential ID without known the appointment token. This vulnerability is fixed in 4.7.19, 5.5.6, and 6.0.1.

INFO

Published Date :

Dec. 5, 2025, 5:16 p.m.

Last Modified :

Dec. 9, 2025, 4:36 p.m.

Remotely Exploit :

No

Source :

[email protected]
Affected Products

The following products are affected by CVE-2025-66546 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Nextcloud calendar
2 Nextcloud notes
: Total Affected Vendor : 1 | Products : 2
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 LOW [email protected]
Solution
Update Nextcloud Calendar app to a patched version.
  • Update Nextcloud Calendar app to 4.7.19 or later.
  • Update Nextcloud Calendar app to 5.5.6 or later.
  • Update Nextcloud Calendar app to 6.0.1 or later.
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2025-66546.

URL Resource
https://github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3 Patch
https://github.com/nextcloud/calendar/pull/7537 Issue Tracking
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95 Patch Vendor Advisory
https://hackerone.com/reports/3275810 Issue Tracking Vendor Advisory
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2025-66546 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2025-66546 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2025-66546 vulnerability anywhere in the article.

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2025-66546 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • Initial Analysis by [email protected]

    Dec. 09, 2025

    Action Type Old Value New Value
    Added CPE Configuration OR *cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* versions from (including) 4.0.0 up to (excluding) 4.7.19 *cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* versions from (including) 5.0.0 up to (excluding) 5.5.6 *cpe:2.3:a:nextcloud:calendar:6.0.0:-:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc1:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc2:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc3:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc4:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc5:*:*:*:*:*:* *cpe:2.3:a:nextcloud:calendar:6.0.0:rc6:*:*:*:*:*:*
    Added Reference Type GitHub, Inc.: https://github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3 Types: Patch
    Added Reference Type GitHub, Inc.: https://github.com/nextcloud/calendar/pull/7537 Types: Issue Tracking
    Added Reference Type GitHub, Inc.: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95 Types: Patch, Vendor Advisory
    Added Reference Type GitHub, Inc.: https://hackerone.com/reports/3275810 Types: Issue Tracking, Vendor Advisory
  • New CVE Received by [email protected]

    Dec. 05, 2025

    Action Type Old Value New Value
    Added Description Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.19, 5.5.6, and 6.0.1, the calendar app allowed blindly booking appointments with a squential ID without known the appointment token. This vulnerability is fixed in 4.7.19, 5.5.6, and 6.0.1.
    Added CVSS V3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
    Added CWE CWE-639
    Added Reference https://github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3
    Added Reference https://github.com/nextcloud/calendar/pull/7537
    Added Reference https://github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95
    Added Reference https://hackerone.com/reports/3275810
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
Vulnerability Scoring Details
Base CVSS Score: 3.3
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact