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CVE-2025-66511

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Date: December 5, 2025

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.

Severity Score

Related Resources (6)

https://github.com/nextcloud/calendar/pull/7659
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27
https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb
https://nvd.nist.gov/vuln/detail/CVE-2025-66511
https://hackerone.com/reports/3385434
https://www.mend.io/vulnerability-database/CVE-2025-66511

Severity Score

Weakness Type (CWE)

Use of Insufficiently Random Values

CWE-330

Top Fix

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Upgrade Version

Upgrade to version https://github.com/nextcloud/calendar.git - v6.0.3

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CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): NONE
Scope (S): UNCHANGED
Confidentiality (C): LOW
Integrity (I): LOW
Availability (A): NONE

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