CVE-2025-66546

Unauthorized appointment booking via sequential configuration IDs

Published Dec 5, 2025 · Updated Dec 5, 2025

Authorization bypass in Nextcloud Calendar before 4.7.19, 5.5.6, or 6.0.1 allows attackers to book appointments without a token. The BookingController appointment routes accepted a sequential configuration ID and resolved it with findById instead of requiring the configuration token. Knowledge or enumeration of the sequential identifier was sufficient to reach appointment slots and submit a booking without the generated token.

CVSS severity3.3
Low
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Nextcloud Calendar before 4.7.19, 5.5.6, or 6.0.1 allows attackers to book appointments without a token. The BookingController appointment routes accepted a sequential configuration ID and resolved it with findById instead of requiring the configuration token. Knowledge or enumeration of the sequential identifier was sufficient to reach appointment slots and submit a booking without the generated token.

The record

CVE
CVE-2025-66546
Published
Dec 5, 2025
Updated
Dec 5, 2025
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-639, T1190
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 3.0.0-beta1, < 4.7.19
  2. Affected versionversion=>= 5.0.0-rc.1, < 5.5.6
  3. Affected versionversion=>= 6.0.0-rc.1, < 6.0.1

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 3.0.0-beta1, < 4.7.19; version=>= 5.0.0-rc.1, < 5.5.6; version=>= 6.0.0-rc.1, < 6.0.1

Published CVSS scores

3.3GitHub, Inc.CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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