6.5

CVE-2025-66511: nextcloud calendar Use of Insufficiently Random Values

CVSS: 6.5v3.1MediumAnalyzed
Published 05-12-2025Last modified 05-12-2025
Open JSON

Vulnerability summary

CVE-2025-66511 is a medium (CVSS 6.5) Use of Insufficiently Random Values vulnerability in nextcloud calendar. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 20.6% of scored vulnerabilities.

Overall risk
26/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.5/10
010
Medium · v3.1 (NVD)
EPSS score
0.29%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 05-12-2025
    PublishedVulnerability first disclosed.
  2. 05-12-2025
    Last modifiedVulnerability information updated.

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 metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

0.29%

Chance of exploitation in the next 30 days

Percentile

21%

Versus all other CVEs

30-day change

0.00 pp

From 0.29% on 18-09-2026

18-09-202618-10-2026
EPSS score
0.29%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Nextcloud2 products

1 vendor · 2 products

References

4 links