Medium severity4.8NVD Advisory· Published Dec 5, 2025· Updated Jun 17, 2026
CVE-2025-66511
CVE-2025-66511
Description
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.
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Affected products
3- Range: >= 6.0.0-rc.1, < 6.0.3
Patches
Vulnerability mechanics
References
4- github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fbnvdPatch
- github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27nvdPatchVendor Advisory
- hackerone.com/reports/3385434nvdPermissions RequiredVendor Advisory
- github.com/nextcloud/calendar/pull/7659nvdIssue Tracking
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