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

> Authenticated users can enumerate other users on the Nextcloud instance via the Calendar app's attendee suggestion endpoint, bypassing sharing restrictions.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Jun 2026
- **Updated:** 1 Jun 2026
- **Also known as:** GHSA-r697-74m9-gvf2

## What is CVE-2026-45286?

CVE-2026-45286 is a medium-severity vulnerability in nextcloud security-advisories, published on 1 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### 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.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-45286?

It affects 1 product.


Products: Nextcloud Calendar.

## How do I fix CVE-2026-45286?

No fix has been published for CVE-2026-45286 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45286 being exploited?

There is no known exploitation of CVE-2026-45286 in the wild and no public exploit code.

## Other vulnerabilities in nextcloud security-advisories

- [CVE-2025-66550](https://insights.sbomify.com/CVE-2025-66550/): Nextcloud Calendar attachments of local files are offered to downloaded (medium 5.7)
- [CVE-2022-24838](https://insights.sbomify.com/CVE-2022-24838/): Command Injection in Appointment Emails for Nextcloud Calendar (medium 5.3)
- [CVE-2025-66511](https://insights.sbomify.com/CVE-2025-66511/): Nextcloud Calendar app used predictable proposal participant tokens (medium 4.8)
- [CVE-2018-3763](https://insights.sbomify.com/CVE-2018-3763/): Cross-site scripting in Nextcloud Calendar application (medium 4.8)
- [CVE-2024-37316](https://insights.sbomify.com/CVE-2024-37316/): Nextcloud Calendar's event create can create attachments that link to other websites (medium 4.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45286 and fix it if it is affected.

What it is: CVE-2026-45286 is a medium-severity vulnerability in nextcloud security-advisories, published on 1 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45286 in the wild and no public exploit code.

Affected product: nextcloud security-advisories. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45286/ (Markdown: https://insights.sbomify.com/CVE-2026-45286/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45286
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45286
- OSV: https://osv.dev/vulnerability/CVE-2026-45286

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45286/
Summaries are generated and may contain mistakes; the official description above is the record.