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CVE-2025-66511

22
FAUCET Score

CVE-2025-66511 impacts Nextcloud Calendar versions prior to 6.0.3, where a flaw in participant token generation allows attackers to compute valid tokens. This enables unauthorized access to meeting proposal details and the submission of dates. Rated as MEDIUM severity with a CVSS score of 6.5, the vulnerability has a low attack complexity and requires no user interaction, potentially leading to unauthorized information disclosure and modification. There is currently no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
>= 6.0.0, < 6.0.3CPE matchmatch criteria
cpe:2.3:a:nextcloud:calendar:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

4.8MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
2.5
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.26%
Probability of exploitation in next 30 days
EPSS Percentile
17.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-26
Model: v2026.06.15
This CVE's current EPSS score of 0.0026 is in the 8th percentile among its peer group of 23,701 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

github.com / nextcloud/calendar/commit/8de14ae87f321f5f09280d9895a27d54d24f33fb
Patch
github.com / nextcloud/calendar/pull/7659
Issue Tracking
github.com / nextcloud/security-advisories/security/advisories/GHSA-whm3-vv55-gf27
PatchVendor Advisory
hackerone.com / reports/3385434
Permissions RequiredVendor Advisory