CVE-2025-66511
Nextcloud Calendar app used predictable proposal participant tokens
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.
INFO
Published Date :
Dec. 5, 2025, 5:16 p.m.
Last Modified :
Dec. 10, 2025, 4:14 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update Nextcloud Calendar app to 6.0.3.
- Verify token generation uses a strong algorithm.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-66511.
| URL | Resource |
|---|---|
| https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb | Patch |
| https://github.com/nextcloud/calendar/pull/7659 | Issue Tracking |
| https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27 | Patch Vendor Advisory |
| https://hackerone.com/reports/3385434 | Permissions Required Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-66511 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-66511
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-66511 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2025-66511 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Dec. 10, 2025
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Added CPE Configuration OR *cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:* versions from (including) 6.0.0 up to (excluding) 6.0.3 Added Reference Type GitHub, Inc.: https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb Types: Patch Added Reference Type GitHub, Inc.: https://github.com/nextcloud/calendar/pull/7659 Types: Issue Tracking Added Reference Type GitHub, Inc.: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27 Types: Patch, Vendor Advisory Added Reference Type GitHub, Inc.: https://hackerone.com/reports/3385434 Types: Permissions Required, Vendor Advisory -
New CVE Received by [email protected]
Dec. 05, 2025
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Added CWE CWE-330 Added Reference https://github.com/nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb Added Reference https://github.com/nextcloud/calendar/pull/7659 Added Reference https://github.com/nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27 Added Reference https://hackerone.com/reports/3385434