What is the CVSS score of CVE-2025-66550?

CVE-2025-66550 has a CVSS 3.1 base score of 5.7 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N. EPSS exploitation probability: 0.0%.

Which versions of Calendar are affected by CVE-2025-66550?

Organizations using Nextcloud Calendar should be aware of moderate risk from CVE-2025-66550 rated CVSS 5.7. Exploitation could compromise the security of affected deployments.. A patch is available.

Is there a public PoC exploit available for CVE-2025-66550?

Yes, a public proof-of-concept exploit is available for CVE-2025-66550. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2025-66550?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Vendor patch is available.

Calendar CVE-2025-66550

EUVD-2025-201443 MEDIUM

Improper Handling of Unexpected Data Type (CWE-241)

2025-12-05 security-advisories@github.com

Information Disclosure Calendar Nextcloud

5.7

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

5.7 MEDIUM

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

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Lifecycle Timeline

EUVD ID Assigned

Mar 15, 2026 - 17:08 euvd

EUVD-2025-201443

Analysis Generated

Mar 15, 2026 - 17:08 vuln.today

Patch released

Mar 15, 2026 - 17:08 nvd

Patch available

PoC Detected

Dec 10, 2025 - 14:13 vuln.today

Public exploit code

CVE Published

Dec 05, 2025 - 17:16 nvd

MEDIUM 5.7

DescriptionGitHub Advisory

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.