How severe is CVE-2025-66546?

CVE-2025-66546 has a CVSS 3.x base score of 3.3, rated low severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2025-66546 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (2nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-66546?

CVE-2025-66546 primarily affects Nextcloud Calendar. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2025-66546?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-66546 have an EU (EUVD) identifier?

Yes. CVE-2025-66546 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201445.

When was CVE-2025-66546 published?

CVE-2025-66546 was published on 2025-12-05 and last updated on 2026-06-17.

CVE-2025-66546

CVE-2025-66546 is a low-severity vulnerability in Nextcloud Calendar with a CVSS 3.x base score of 3.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-639.

Key facts

Severity: Low (CVSS 3.x base score 3.3)
EPSS exploit prediction: 0% (2nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-201445
Weakness: CWE-639
Affected product: Nextcloud Calendar
Published: 2025-12-05
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-66546?: 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.
How severe is CVE-2025-66546?: CVE-2025-66546 has a CVSS 3.x base score of 3.3, rated low severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2025-66546 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (2nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-66546?: CVE-2025-66546 primarily affects Nextcloud Calendar. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-66546?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-66546 have an EU (EUVD) identifier?: Yes. CVE-2025-66546 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201445.
When was CVE-2025-66546 published?: CVE-2025-66546 was published on 2025-12-05 and last updated on 2026-06-17.

References

Affected products (8)

cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:-:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc1:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc2:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc3:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc4:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc5:*:*:*:*:*:*
cpe:2.3:a:nextcloud:calendar:6.0.0:rc6:*:*:*:*:*:*

More vulnerabilities in Nextcloud Calendar

CVE-2025-66550 — Medium (CVSS 5.7): Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar…
CVE-2022-24838 — Medium (CVSS 5.3): Nextcloud Calendar is a calendar application for the nextcloud framework. SMTP Command Injection in Appointment Emails…
CVE-2025-66511 — Medium (CVSS 4.8): Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for…
CVE-2018-3763 — Medium (CVSS 4.8): In Nextcloud Calendar before 1.5.8 and 1.6.1, a missing sanitization of search results for an autocomplete field could…
CVE-2024-37316 — Medium (CVSS 4.6): Nextcloud Calendar is a calendar app for Nextcloud. Authenticated users could create an event with manipulated…
CVE-2026-45286 — Medium (CVSS 4.3): Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before…

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