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Vulnerability record · CVE-2025-66550 · published 5 December 2025

CVE-2025-66550: Nextcloud calendar vulnerability

Nextcloud · Calendar

Nextcloud 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 attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.

5.7 CVSS 3.1 Medium EPSS 0.34% · top 75.0% CWE-241 · CWE-241
5.7CVSS 3.1 base score
0.34%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 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/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/63a6c398db01391eb9fd5297a0d4c3d6e614f769 Patch
https://github.com/nextcloud/calendar/pull/6971 Issue Tracking
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-f29c-ppmv-8mcv PatchVendor Advisory
https://hackerone.com/reports/3112033 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%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%4.3CVE-2023-33183Nextcloud calendar improper authorization vulnerabilityCalendar app for Nextcloud easily sync events from various devices with your Nextcloud. Some internal paths of the website are disclosed when the SMT…EPSS 0.44%

Source: NIST National Vulnerability Database (record CVE-2025-66550), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.