CVE-2025-66550

5.7 MEDIUM 0.4% exploit odds Fix listed Other Server

What it is

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.

At a glance

Exploitability: Can be exploited over the network with a low-privilege account, but needs a user to act. High risk of data tampering.
Exploit odds: 0.4% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2025-12-05 17:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-18 14:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.4% in the next 30 days (EPSS).
Severity: 5.7 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2025-12-05 17:16 UTC
Last modified: 2026-10-18 14:10 UTC
Exploit probability: 0.4% · EPSS, next 30 days
Weakness: CWE-241
Record status: Analyzed

Affected

Nextcloud Calendar < 4.7.17
Nextcloud Calendar < 5.2.4

Attack profile CVSS 3.1 · 5.7

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: Required
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2025-66550.md and follow it. Check whether this project is affected by CVE-2025-66550. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record