CVE-2025-66546: nextcloud security-advisories · Insecure Direct Object Reference
Affects nextcloud security-advisoriesSource CVE Database V5
Not known to be exploited · CVSS 3.3 Low · fixed in 6.0.1 : update nextcloud security-advisories when convenient.
Data as of 26 Oct 2026, 06:26 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 6.0.1, 5.5.6, 4.7.19
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 5 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.
What to do
Upgrade nextcloud/calendar to 6.0.1, 5.5.6 or 4.7.19.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
GitHubnextcloud/calendarpkg:github/nextcloud/calendarOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
European organizations should promptly update Nextcloud Calendar to versions 4.7.19, 5.5.6, or 6.0.1 or later to remediate this vulnerability. Beyond patching, administrators should enforce strict access controls to limit local access to trusted users only, reducing the risk of exploitation by low-privilege attackers. Monitoring calendar booking activities for unusual patterns, such as rapid sequential appointment creation, can help detect exploitation attempts. Implementing multi-factor authentication and strong user account management will reduce the likelihood of unauthorized local access. Additionally, reviewing and hardening the configuration of Nextcloud instances to restrict API access and enforce token validation mechanisms can mitigate similar authorization bypass risks. Regular security audits and user training on insider threat awareness will further reduce exposure.
Description
Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.19, 5.5.6, and 6.0.1, the calendar app allowed blindly booking appointments with a squential ID without known the appointment token. This vulnerability is fixed in 4.7.19, 5.5.6, and 6.0.1.
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95 (opens in a new tab)
- github.com/nextcloud/calendar/pull/7537 (opens in a new tab)
- github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3 (opens in a new tab)
- hackerone.com/reports/3275810 (opens in a new tab)