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TI-2025-40961 Aliases CVE-2025-66550

Nextcloud Calendar attachments of local files are offered to downloaded

Priority LOW 26CWE-241Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
Required
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00366 30th percentileScored 2026-11-07
Fix Fixed security-advisories (nextcloud): 5.2.4, 4.7.17

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
nextcloudsecurity-advisories5.0.0-rc.1 to before 5.2.4; before 4.7.175.2.4, 4.7.17Patch availableCNA
  • security-advisories Vendornextcloud Affected 5.0.0-rc.1 to before 5.2.4; before 4.7.17 Fixed in 5.2.4, 4.7.17 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*4.0.0 to before 4.7.17; 5.0.0 to before 5.2.4Vulnerablenextcloud
  • cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* Versions 4.0.0 to before 4.7.17; 5.0.0 to before 5.2.4 Vulnerable ·nextcloud

Remediation

  • Fix · CNA security-advisories (nextcloud) Fixed in 5.2.4, 4.7.17

Timeline

  1. 2026-10-02 Threatist record created from CVE-2025-66550

References

Patch 2

Advisory 1

Other 1

  • TI-2022-08650 Command Injection in Appointment Emails for Nextcloud Calendar CVSS 3.1CRITICAL 9.8
  • TI-2023-24171 Inviting excessive long email addresses to a calendar event makes the Nextcloud server unresponsive CVSS 3.1MEDIUM 4.3
  • TI-2023-26171 Calendar app returns full stacktrace when an error happens while editing appointment CVSS 3.1MEDIUM 6.5
  • TI-2025-40933 Nextcloud Calendar app used predictable proposal participant tokens CVSS 3.1MEDIUM 6.5
  • TI-2018-02759 Cross-site scripting in Nextcloud Calendar application CVSS 3.1MEDIUM 4.8
  • TI-2024-24828 Nextcloud Calendar's event create can create attachments that link to other websites CVSS 3.1MEDIUM 4.6
See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences