Vulnerability Report

CVE-2025-66550

Title: Crafted attachment in Nextcloud Calendar can trigger unconfirmed download

Other

Proof Of Concept

No public PoC currently indexed for CVE-2025-66550.

CWE Category CWE-241

Published Date Dec 05, 2025

Modified Date Dec 10, 2025

Exploit Status Not Found

Score 5.7 CVSS v3.1

Exploit Probability (EPSS)

0.29%

Vulnerability Summary

CVE-2025-66550: 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.

Impacted Vendors

karen_stevenson 1

nextcloud 1

Reference Links

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

CVSS v3.1

Source Entity [email protected]

Severity MEDIUM

5.7

Attack Vector

NETWORK

Complexity

LOW

Privileges

N/A

Interaction

REQUIRED

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2025-66550 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

December 10, 2025 MODIFIED

Vulnerability data or affected products updated.

December 10, 2025 MODIFIED

Vulnerability data updated via NVD.

December 05, 2025 PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector NETWORK

Complexity LOW

Privileges N/A

Interaction REQUIRED

CVSS Vector String


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

Affected Stack

No specific products linked.