Medium severity · published Jun 1, 2026
CVE-2026-45286
Nextcloud: Calendar app leaked user identifiers via attendee suggestion endpoint
4.3
CVSS
0.3%
EPSS
No
On KEV
Description
Nextcloud is an open source content collaboration platform. From versions 5.5.13 to before 5.5.17, and 6.2.0 to before 6.2.3, an authenticated user can enumerate users on the same Nextcloud instance by using the Calendar app's endpoint for suggesting attendees. The sharing restrictions, applied to other endpoints, were not effective here. This issue has been patched in versions 5.5.17 and 6.2.3.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
Low
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SE
security-advisories · nextcloud
>= 5.5.13, < 5.5.17; >= 6.2.0, < 6.2.3 · source: vendor
CA
Calendar · Nextcloud
5.5.13 before 5.5.17; 6.2.0 before 6.2.3 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45286
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-45286
Exploit
https://github.com/nextcloud/calendar/issues/7971
Issue Tracking
https://github.com/nextcloud/calendar/pull/8197
Mitigation
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-r697-74m9-gvf2
Permissions Required
https://hackerone.com/reports/3540663
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