Nextcloud: Calendar app leaked user identifiers via attendee suggestion endpoint

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Summary

CVECVE-2026-45286
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-01 19:16:50 UTC
Updated2026-06-03 20:35:59 UTC
DescriptionNextcloud 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS: 0.000170000 probability, percentile 0.042090000 (date 2026-06-07)

Problem Types: CWE-200 | NVD-CWE-noinfo | CWE-200 CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
3.1CNADECLARED4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Nextcloud Calendar All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Nextcloud Security-advisories affected >= 5.5.13, < 5.5.17 Not specified
CNA Nextcloud Security-advisories affected >= 6.2.0, < 6.2.3 Not specified

References

ReferenceSourceLinkTags
github.com/nextcloud/security-advisories/security/advisories/GHSA-r697-7... [email protected] github.com Mitigation, Vendor Advisory
hackerone.com/reports/3540663 [email protected] hackerone.com Permissions Required
github.com/nextcloud/calendar/issues/7971 [email protected] github.com Exploit, Issue Tracking, Patch
github.com/nextcloud/calendar/pull/8197 [email protected] github.com Issue Tracking, Patch
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