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

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.

Published: 2025-12-05 Last update: 2025-12-09 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-66546 is rated Low Risk (13.6/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.01%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-66546

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-12-06 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-66546

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
3.3 3.1 LOW
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 1.8 1.4 [email protected]

Weakness enumeration for CVE-2025-66546

Affected software / configurations for CVE-2025-66546

Vendor Product Version Raw CPE
nextcloud calendar >= 4.0.0, < 4.7.19 cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*
nextcloud calendar >= 5.0.0, < 5.5.6 cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:-:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc1:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc2:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc3:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc4:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc5:*:*:*:*:*:*
nextcloud calendar 6.0.0 cpe:2.3:a:nextcloud:calendar:6.0.0:rc6:*:*:*:*:*:*

References for CVE-2025-66546

cvelogic Threat Intelligence