How severe is CVE-2025-66550?

CVE-2025-66550 has a CVSS 3.x base score of 5.7, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2025-66550 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-66550?

CVE-2025-66550 affects Nextcloud Calendar. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-66550?

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

Does CVE-2025-66550 have an EU (EUVD) identifier?

Yes. CVE-2025-66550 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201443.

When was CVE-2025-66550 published?

CVE-2025-66550 was published on 2025-12-05 and last updated on 2026-06-17.

CVE-2025-66550

CVE-2025-66550 is a medium-severity vulnerability in Nextcloud Calendar with a CVSS 3.x base score of 5.7. 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-241.

Key facts

Severity: Medium (CVSS 3.x base score 5.7)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-201443
Weakness: CWE-241
Affected product: Nextcloud Calendar
Published: 2025-12-05
Last modified: 2026-06-17

Description

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.

Frequently asked questions

What is CVE-2025-66550?: Nextcloud Calendar is a calendar app for Nextcloud. Prior to 4.7.17 and 5.2.4, when a malicious user creates a calendar event with a crafted attachment that links to a download link of a file on the same Nextcloud server, the file would be downloaded without the user confirming the action. This vulnerability is fixed in 4.7.17 and 5.2.4.
How severe is CVE-2025-66550?: CVE-2025-66550 has a CVSS 3.x base score of 5.7, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2025-66550 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-66550?: CVE-2025-66550 affects Nextcloud Calendar. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-66550?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-66550 have an EU (EUVD) identifier?: Yes. CVE-2025-66550 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-201443.
When was CVE-2025-66550 published?: CVE-2025-66550 was published on 2025-12-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*

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