# CVE-2025-66550

## Summary

- **CVE ID:** CVE-2025-66550
- **Severity:** MEDIUM
- **CVSS Score:** 5.7 (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N)
- **CWE:** CWE-241
- **Published:** Dec 5, 2025
- **Last Modified:** Mar 13, 2026

## 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.

## Affected Products

- nextcloud — security-advisories (>= 5.0.0-rc.1, < 5.2.4)
- nextcloud — security-advisories (< 4.7.17)

## References

- [CNA](https://github.com/nextcloud/security-advisories/security/advisories/GHSA-f29c-ppmv-8mcv)
- [CNA](https://github.com/nextcloud/calendar/pull/6971)
- [CNA](https://github.com/nextcloud/calendar/commit/63a6c398db01391eb9fd5297a0d4c3d6e614f769)
- [CNA](https://hackerone.com/reports/3112033)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.34%
- **EPSS Percentile:** 27.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._