CVE-2025-66511

Nextcloud Calendar app used predictable proposal participant tokens

CVSS 4.8 MEDIUMEPSS 0.2%CWE-330

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 4.8EPSS 0.2%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

05 Dec 2025Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected products

nextcloud · security-advisories

Want to know if your infrastructure is exposed to this?

Talk to TrueHacking →

References

https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb https://github.com/nextcloud/calendar/pull/7659 https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27 https://hackerone.com/reports/3385434