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CVE-2025-66511

Nextcloud Calendar app used predictable proposal participant tokens

Published: Dec 5, 2025Updated: Dec 10, 2025 Sources: CVE List NVD BDUCWE-330
NVD MITRE
4.8CVSSMEDIUM
EPSS Score
0.2%
Top 84.5%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:HPR:NUI:NS:UC:LI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:LConfidentiality
Low
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-330

Affected Products

calendarnextcloud
On-prem
Cloud & SaaS / saas-application
security-advisoriesnextcloud
SaaSSaaS Service
Cloud & SaaS / saas-application
РЕД ОСООО «Ред Софт»
On-premOS
Operating Systems / linux-distro
Nextcloud CalendarNextcloud GmbH
SaaS
Cloud & SaaS / saas-application
nextcloudoss-projectDECloud & SaaSaka nextcloud server
ооо «ред софт»commercialRUOperating Systemsaka red soft
nextcloud gmbhcommercialDECloud & SaaSaka nextcloud server, nextcloud enterprise server, nextcloud calendar

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Credential Access
View detailed technique mapping

References

https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb
github.com
https://github.com/nextcloud/calendar/pull/7659
github.com
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27
github.com
and 3 more references View all →

Timeline

Published
Dec 5, 2025
Last Updated
Dec 10, 2025

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