Improper Handling of Unexpected Data Type in Nextcloud Calendar - CVE-2025-66550
Published: December 8, 2025
Vulnerability identifier: #VU119259
CSH Severity: Medium
CVSS v4: 6.8 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2025-66550
CWE-ID: CWE-241
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to compromise the target system.
The vulnerability exists due to improper handling of unexpected data type. A remote user can create a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server and download the file without the user confirming the action.
Affected software
Nextcloud Calendar
How to mitigate CVE-2025-66550
Install updates from vendor's website.
Nextcloud Calendar - addressed in versions 4.7.17, 5.2.4