Is CVE-2025-66550 in the CISA KEV catalog?

No. CVE-2025-66550 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2025-66550?

CVE-2025-66550 has a CVSS v3 base score of 5.7 (MEDIUM).

What is the EPSS score for CVE-2025-66550?

CVE-2025-66550 has an EPSS score of 0.29% (21th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2025-66550?

Upgrade calendar to 5.2.4 or later.

CVE & CISA-KEV Catalog

CVE-2025-66550

MEDIUM

5.7

CVSS v3

NVD

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.

CWE-241

How to fix

Remediation Available

calendarNVD

Affected:>= 5.0.0, < 5.2.4Fixed in:5.2.4CVE-2025-66550derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N

Exploit Intelligence

0.29%probability of exploitation in 30 days

21stpercentile

Low risk: more likely to be exploited than 21% of all known CVEs.

References

Patch2

Vendor Advisory1

hackerone.com

Issue Tracking1

github.com

Related Vulnerabilities

Other CWE-241 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-30591	High	7.5	54%	-	-
CVE-2022-29181	High	8.2	3.1%	-	Fix
CVE-2021-39131	High	7.5	1.9%	-	-
CVE-2021-40116	High	8.6	1.3%	-	Fix
CVE-2022-24668	High	7.5	1.1%	-	Fix
CVE-2021-32696	Low	3.7	1.1%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-12-10.