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Medium severity · published Dec 5, 2025
CVE-2025-66550
Nextcloud Calendar attachments of local files are offered to downloaded
5.7
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 27% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SE
security-advisories · nextcloud
>= 5.0.0-rc.1, < 5.2.4; < 4.7.17 · source: vendor
CA
Calendar · Nextcloud
4.0.0 before 4.7.17; 5.0.0 before 5.2.4 · source: NVD
Affected product
SE
security-advisories
nextcloud
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66550
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-66550
Patch
https://github.com/nextcloud/calendar/commit/63a6c398db01391eb9fd5297a0d4c3d6e614f769
Issue Tracking
https://github.com/nextcloud/calendar/pull/6971
Patch
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-f29c-ppmv-8mcv
Issue Tracking
https://hackerone.com/reports/3112033
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