Vulnerability Report

CVE-2025-66511

Title: Nextcloud Calendar Predictable Participant Tokens

Other

Proof Of Concept

No public PoC currently indexed for CVE-2025-66511.

CWE Category CWE-330
Published Date Dec 05, 2025
Modified Date Dec 10, 2025
Exploit Status Not Found
Score 4.8 CVSS v3.1
Exploit Probability (EPSS)
0.26%

Vulnerability Summary

CVE-2025-66511: 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.

Impacted Vendors

K
karen_stevenson 1
N
nextcloud 1

Reference Links

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
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
4.8
Attack Vector
NETWORK
Complexity
HIGH
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
6.5
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2025-66511 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

MODIFIED

Vulnerability data or affected products updated.

MODIFIED

Vulnerability data updated via NVD.

PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity HIGH
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected Stack

No specific products linked.