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TI-2025-40933 Aliases CVE-2025-66511

Nextcloud Calendar app used predictable proposal participant tokens

Priority LOW 29CWE-330Published · Updated

Key facts

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

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

Summary

Nextcloud Calendar is a calendar app for Nextcloud. Prior to 6.0.3, the Calendar app generates participant tokens for meeting proposals using a hash function, allowing an attacker to compute valid participant tokens, which allowed them to request details and submit dates in meeting proposals. The tokens are not purely random generated. This vulnerability is fixed in 6.0.3.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00316 24th percentileScored 2026-11-07
Fix Fixed security-advisories (nextcloud): 6.0.3

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-advisories6.0.0-rc.1 to before 6.0.36.0.3Patch availableCNA
  • security-advisories Vendornextcloud Affected 6.0.0-rc.1 to before 6.0.3 Fixed in 6.0.3 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*6.0.0 to before 6.0.3Vulnerablenextcloud
  • cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* Versions 6.0.0 to before 6.0.3 Vulnerable ·nextcloud

Remediation

  • Fix · CNA security-advisories (nextcloud) Fixed in 6.0.3

Timeline

  1. 2026-10-02 Threatist record created from CVE-2025-66511

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-2025-40961 Nextcloud Calendar attachments of local files are offered to downloaded CVSS 3.1MEDIUM 5.7
  • 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