Vulnerability · Published Jun 1, 2026 · Assigned by GitHub_M

CVE-2026-45286Nextcloud: Calendar app leaked user identifiers via attendee suggestion endpoint

Medium 4.3

In plain English

A medium-severity information exposure in security-advisories from nextcloud. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities).

Severity (CVSS 3.1)4.3Medium

Exploit odds (30 days)0.3%top 79.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
nextcloud	security-advisories	>= 5.5.13, < 5.5.17>= 6.2.0, < 6.2.3

Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

References

https://github.com/nextcloud/security-advisories/security/advisories/GHSA-r697-74m9-gvf2 x_refsource_CONFIRM
https://github.com/nextcloud/calendar/issues/7971 x_refsource_MISC
https://github.com/nextcloud/calendar/pull/8197 x_refsource_MISC
https://hackerone.com/reports/3540663 x_refsource_MISC