CVE-2025-665505.7MediumCWE-241

CVE-2025-66550: Nextcloud Calendar attachments of local files are offered to downloaded

nextcloud · security-advisories

Affected: nextcloud security-advisories · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.4%probability of exploitation in the next 30 days

30th percentile

050100

Higher than 30% of scored CVEs

5.7MediumCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

nextcloud · security-advisories>= 5.0.0-rc.1, < 5.2.4; < 4.7.17

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Improper Handling of Unexpected Data Type · Input Validation and Logic
Vendor: nextcloud
Published: December 2025
Band: Unlikely (under 1%), December 2025
Bounty reports: 1 disclosed on HackerOne

Disclosed bug bounty reports about CVE-2025-66550

The reports on HackerOne that name this CVE, with HackerOne's own outcome. Titles and metadata only.

Calendar attachments of local files are offered to downloadedNextcloud · 2025 · medium severityValid

CoverageNo articles yet

No CyberSIXT article names CVE-2025-66550 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.