CVE-2026-45286: CWE-200: Exposure of Sensitive Information to an Unauthorized Actor in nextcloud security-advisories
Nextcloud versions 5.5.13 to before 5.5.17 and 6.2.0 to before 6.2.3 contain a vulnerability where an authenticated user can enumerate other users on the same instance via the Calendar app's attendee suggestion endpoint. This endpoint did not enforce sharing restrictions that were applied elsewhere, leading to exposure of user information.
AI Analysis
Technical Summary
CVE-2026-45286 is an information exposure vulnerability in Nextcloud's Calendar app affecting versions 5.5.13 to <5.5.17 and 6.2.0 to <6.2.3. Authenticated users could enumerate other users on the same Nextcloud instance through the attendee suggestion endpoint, bypassing sharing restrictions that were effective on other endpoints. This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The flaw has been patched in versions 5.5.17 and 6.2.3.
Potential Impact
An authenticated user on a vulnerable Nextcloud instance can obtain information about other users by enumerating them via the Calendar app's endpoint. This exposure is limited to user enumeration and does not affect confidentiality, integrity, or availability beyond this information disclosure. The CVSS score of 4.3 reflects a medium severity impact with low complexity and no user interaction required.
Mitigation Recommendations
Upgrade Nextcloud to version 5.5.17 or later, or 6.2.3 or later, where this vulnerability has been patched. Since this is not a cloud service, administrators must apply these updates manually. Patch status is confirmed by the vendor advisory stating the fix is included in these versions.
CVE-2026-45286: CWE-200: Exposure of Sensitive Information to an Unauthorized Actor in nextcloud security-advisories
Description
Nextcloud versions 5.5.13 to before 5.5.17 and 6.2.0 to before 6.2.3 contain a vulnerability where an authenticated user can enumerate other users on the same instance via the Calendar app's attendee suggestion endpoint. This endpoint did not enforce sharing restrictions that were applied elsewhere, leading to exposure of user information.
CVSS v3.1
Score 4.3medium
Affected software
pkg:github/nextcloud/calendarRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-45286 is an information exposure vulnerability in Nextcloud's Calendar app affecting versions 5.5.13 to <5.5.17 and 6.2.0 to <6.2.3. Authenticated users could enumerate other users on the same Nextcloud instance through the attendee suggestion endpoint, bypassing sharing restrictions that were effective on other endpoints. This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The flaw has been patched in versions 5.5.17 and 6.2.3.
Potential Impact
An authenticated user on a vulnerable Nextcloud instance can obtain information about other users by enumerating them via the Calendar app's endpoint. This exposure is limited to user enumeration and does not affect confidentiality, integrity, or availability beyond this information disclosure. The CVSS score of 4.3 reflects a medium severity impact with low complexity and no user interaction required.
Mitigation Recommendations
Upgrade Nextcloud to version 5.5.17 or later, or 6.2.3 or later, where this vulnerability has been patched. Since this is not a cloud service, administrators must apply these updates manually. Patch status is confirmed by the vendor advisory stating the fix is included in these versions.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-11T20:14:43.200Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a1de306e29bf47b503a558a
Added to database: 06/01/2026, 19:52:38 UTC
Last enriched: 06/08/2026, 21:08:11 UTC
Last updated: 07/31/2026, 19:22:59 UTC
Views: 98
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