What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-06-01 · updated 2026-07-22
• Weakness: CWE-200

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

• Nextcloud Calendar application: from 5.5.13 before 5.5.17; from 6.2.0 before 6.2.3 — fixed in 5.5.17, 6.2.3

How to fix

Upgrade to a fixed version: Nextcloud Calendar application 5.5.17, 6.2.3. Check the vendor advisory for mitigations.

References

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

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