CVE-2025-66550: calendar — Fix

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.

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CVSS v3.1 Score

5.7

MEDIUM

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

Weakness Type (CWE)

CWE-241 CWE-241

Affected Products

Vendor	Product	Versions
nextcloud	calendar	4.0.0 — 4.7.17
nextcloud	calendar	5.0.0 — 5.2.4

References

Advisories & Patches

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

Other References

https://github.com/nextcloud/calendar/pull/6971

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 5.7 (MEDIUM).

How severe is CVE-2025-66550? +

CVE-2025-66550 has a CVSS v3.1 score of 5.7 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-66550? +

CVE-2025-66550 affects products from nextcloud, specifically: calendar. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-66550? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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