CVE-2025-66511
low-risk
Published 2025-12-05
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.
Do I need to act?
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0.03% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
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Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
4
CVSS 4.8/10
Medium
NETWORK
/ HIGH complexity
Affected Products (1)
Calendar
Affected Vendors
References (4)
Issue Tracking
https://github.com/nextcloud/calendar/pull/7659
Permissions Required
https://hackerone.com/reports/3385434
20
/ 100
low-risk
Severity
15/34 · Moderate
Exploitability
0/34 · Minimal
Exposure
5/34 · Minimal