PT-2025-49289 · Nextcloud+1 · Nextcloud Calendar+1

Published 2025-12-05 · Updated 2026-02-09 · CVE-2025-66546

Positive Technologies (AI Summary)

CVSS v3.1

3.3

Low

Base vector

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

Name of the Vulnerable Software and Affected Versions Nextcloud Calendar versions prior to 4.7.19 Nextcloud Calendar versions prior to 5.5.6 Nextcloud Calendar versions prior to 6.0.1

Description The Nextcloud Calendar application contained a flaw where appointments could be booked without knowing the appointment token, by using a sequential ID. This allowed for potentially unauthorized scheduling of calendar events.

Recommendations Update Nextcloud Calendar to version 4.7.19 or later. Update Nextcloud Calendar to version 5.5.6 or later. Update Nextcloud Calendar to version 6.0.1 or later.

Exploit

Fix

IDOR

Weakness Enumeration

CWE-639

Related Identifiers

BDU:2026-03580

CVE-2025-66546

GHSA-7X2J-2674-FJ95

Affected Products

Nextcloud Calendar

Red Os

References · 15

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/66xxx/CVE-2025-66546.json · Exploit
• https://github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3 · Patch
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95 · Vendor Advisory
• https://bdu.fstec.ru/vul/2026-03580 · Security Note
• https://nvd.nist.gov/vuln/detail/CVE-2025-66546 · Security Note
• https://osv.dev/vulnerability/CVE-2025-66546 · Vendor Advisory
• https://hackerone.com/reports/3275810 · Vendor Advisory
• https://github.com/nextcloud/calendar/pull/7537 · Note
• https://t.me/cveNotify/145225 · Telegram Post
• https://redos.red-soft.ru/support/secure/uyazvimosti/uyazvimost-nextcloud-app-calendar-cve-2025-66546-7.3/?sphrase_id=1456287 · Note
• https://twitter.com/CVEnew/status/1996994593099841995 · Twitter Post
• https://twitter.com/VulmonFeeds/status/1997010014179893340 · Twitter Post
• https://redos.red-soft.ru/support/secure/uyazvimosti/support/secure/uyazvimosti-red-os-8-0/uyazvimost-nextcloud-app-calendar-cve-2025-66546-8.0 · Note
• https://redos.red-soft.ru/support/secure/uyazvimosti/support/secure/uyazvimosti/uyazvimost-nextcloud-app-calendar-cve-2025-66546-7.3 · Note
• https://twitter.com/dailycve/status/1998491135329878331 · Twitter Post