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CVE-2025-66546VulnerabilityPublished

CVE-2025-66546: nextcloud security-advisories · Insecure Direct Object Reference

Affects nextcloud security-advisoriesSource CVE Database V5

0

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

CVSS 3.1 base score
3.3Low
How severe the flaw is on the 0–10 CVSS scale.
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:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 5 Dec 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

ProductAffectedFixed in
GitHubnextcloud/calendarpkg:github/nextcloud/calendarOther threatsAffected
  • <4.7.19
  • <5.5.6
  • <6.0.1
Fixed in
  • 4.7.19
  • 5.5.6
  • 6.0.1

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

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