# CVE-2026-3473: Improper file ownership validation in the Boards API allows unauthorised file access

> CVE-2026-3473: Improper file ownership validation in the Boards API allows unauthorised file access. CVSS 5.9 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-3473
Last updated: 2026-07-23T16:10:00Z

- Published: 2026-05-22 10:27 UTC · Updated: 2026-07-23 16:10 UTC · Assigner: Mattermost
- CVSS: 5.9 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
- EPSS: 0.15%, 4th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-639

## Description

Mattermost versions 11.6.x \<= 11.6.0, 11.5.x \<= 11.5.3, 11.4.x \<= 11.4.4, 10.11.x \<= 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs.. Mattermost Advisory ID: MMSA-2026-00620

## Affected vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-3473)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-3473)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-3473 · Markdown: https://rewindex.com/cve/CVE-2026-3473.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-3473 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:06:43.206Z