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Vulnerability record · CVE-2025-66546 · published 5 December 2025

CVE-2025-66546: Nextcloud calendar insecure direct object reference vulnerability

Nextcloud · Calendar

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.

3.3 CVSS 3.1 Low EPSS 0.14% · top 97.3% CWE-639 · Insecure direct object reference
3.3CVSS 3.1 base score
0.14%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
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 PatchVendor Advisory
https://hackerone.com/reports/3275810 Issue TrackingVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2022-24838Nextcloud calendar injection vulnerabilityNextcloud Calendar is a calendar application for the nextcloud framework. SMTP Command Injection in Appointment Emails via Newlines: as newlines and …EPSS 33%6.5CVE-2025-66511Nextcloud calendar vulnerabilityNextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for meeting proposals using a hash …EPSS 0.30%6.5CVE-2023-48308Nextcloud calendar vulnerabilityNextcloud/Cloud is a calendar app for Nextcloud. An attacker can gain access to stacktrace and internal paths of the server when generating an except…EPSS 0.55%5.7CVE-2025-66550Nextcloud calendar vulnerabilityNextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachme…EPSS 0.34%4.8CVE-2018-3763Nextcloud calendar cross-site scripting vulnerabilityIn Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could lead to a stored XSS requiring…EPSS 0.61%4.6CVE-2024-37316Nextcloud calendar vulnerabilityNextcloud Calendar is a calendar app for Nextcloud. Authenticated users could create an event with manipulated attachment data leading to a bad redir…EPSS 0.36%4.3CVE-2026-45286Nextcloud calendar information exposure vulnerabilityNextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user c…EPSS 0.46%4.3CVE-2023-45150Nextcloud calendar uncontrolled resource consumption vulnerabilityNextcloud calendar is a calendar app for the Nextcloud server platform. Due to missing precondition checks the server was trying to validate strings …EPSS 0.39%

Source: NIST National Vulnerability Database (record CVE-2025-66546), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.