Token Generation Vulnerability in Nextcloud Calendar App
CVE-2025-66511

4.8MEDIUM

Key Information:

Vendor

Nextcloud
Status
Security-advisories
Vendor
CVE Published:
5 December 2025

What is CVE-2025-66511?

The Nextcloud Calendar app, prior to version 6.0.3, contains a vulnerability where participant tokens for meeting proposals are generated using a predictable hash function. This weakness allows an attacker to compute valid participant tokens, enabling unauthorized access to meeting details and the ability to propose dates. The issue has been addressed in version 6.0.3, which mitigates the risk associated with token generation.

Human OS v1.0:
Ageing Is an Unpatched Zero-Day Vulnerability.

Remediate biological technical debt. Prime Ageing uses 95% high-purity SIRT6 activation to maintain genomic integrity and bolster systemic resilience.

Deploy the Patch

Affected Version(s)

security-advisories >= 6.0.0-rc.1, < 6.0.3

References

https://github.com/nextcloud/security-advisories/security...
x_refsource_CONFIRM
https://github.com/nextcloud/calendar/pull/7659
x_refsource_MISC
https://github.com/nextcloud/calendar/commit/8de14ae87f32...
x_refsource_MISC

CVSS V3.1

Score:
4.8
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

JSON
.