SB2025120819 - Improper Handling of Unexpected Data Type in Nextcloud Calendar
Published: December 8, 2025
Security Bulletin ID
SB2025120819
CSH Severity
Medium
Patch available
YES
Number of vulnerabilities
1
Exploitation vector
Remote access
Highest impact
Information disclosure
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 1 vulnerability.
1) Improper Handling of Unexpected Data Type (CVE-ID: CVE-2025-66550)
CWE-ID: CWE-241 - Improper Handling of Unexpected Data Type
CVSSv4: 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/E:U/U:Green
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.
Remediation
Install update from vendor's website.