CVE-2026-45286: CWE-200: Exposure of Sensitive Information to an Unauthorized Actor in nextcloud security-advisories
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.
AI Analysis
Technical Summary
This vulnerability (CVE-2026-45286) affects Nextcloud's Calendar app in specific versions, allowing authenticated users to enumerate other users on the same Nextcloud instance by exploiting an endpoint used for suggesting attendees. The flaw arises because sharing restrictions that prevent unauthorized data access on other endpoints were not applied here. This results in exposure of sensitive user information to unauthorized actors within the same instance. The vulnerability is classified under CWE-200 (Exposure of Sensitive Information). It has a CVSS 3.1 base score of 4.3, indicating a medium severity level. The issue has been patched in Nextcloud 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 through the Calendar app's attendee suggestion endpoint. This exposure of sensitive user information could aid in further targeted attacks or privacy violations. There is no indication of impact on data integrity or availability. No known exploits in the wild have been reported.
Mitigation Recommendations
This vulnerability has been patched in Nextcloud versions 5.5.17 and 6.2.3. Users should upgrade to these or later versions to remediate the issue. Since this is not a cloud service, remediation depends on applying the official patches. Patch status is confirmed by the vendor advisory. No additional mitigation steps are indicated.
CVE-2026-45286: CWE-200: Exposure of Sensitive Information to an Unauthorized Actor in nextcloud security-advisories
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 v3.1
Score 4.3medium
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-45286) affects Nextcloud's Calendar app in specific versions, allowing authenticated users to enumerate other users on the same Nextcloud instance by exploiting an endpoint used for suggesting attendees. The flaw arises because sharing restrictions that prevent unauthorized data access on other endpoints were not applied here. This results in exposure of sensitive user information to unauthorized actors within the same instance. The vulnerability is classified under CWE-200 (Exposure of Sensitive Information). It has a CVSS 3.1 base score of 4.3, indicating a medium severity level. The issue has been patched in Nextcloud 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 through the Calendar app's attendee suggestion endpoint. This exposure of sensitive user information could aid in further targeted attacks or privacy violations. There is no indication of impact on data integrity or availability. No known exploits in the wild have been reported.
Mitigation Recommendations
This vulnerability has been patched in Nextcloud versions 5.5.17 and 6.2.3. Users should upgrade to these or later versions to remediate the issue. Since this is not a cloud service, remediation depends on applying the official patches. Patch status is confirmed by the vendor advisory. No additional mitigation steps are indicated.
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: 6/1/2026, 7:52:38 PM
Last enriched: 6/1/2026, 8:04:55 PM
Last updated: 6/2/2026, 4:58:41 AM
Views: 4
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.