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

Published May 22, 2026
·
Updated

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 Software

1 affected component
Mattermost Mattermost<=11.6.0, <=11.5.3, <=11.4.4, <=10.11.14

Remediation

Information

Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

Event History

May 22, 2026
CVE Published
via MITRE·10:27 AM
Data Sourced
via MITRE·10:27 AM
RemedyDescriptionSeverityWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-3473?

The severity of CVE-2026-3473 is categorized as medium with a score of 5.9.

2

How do I fix CVE-2026-3473?

To fix CVE-2026-3473, update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

3

What issue does CVE-2026-3473 highlight in Mattermost?

CVE-2026-3473 highlights an improper file ownership validation issue in the Boards API that allows unauthorized file access.

4

Who is affected by CVE-2026-3473?

CVE-2026-3473 affects Mattermost versions 11.6.x through 11.6.0, 11.5.x through 11.5.3, 11.4.x through 11.4.4, and 10.11.x through 10.11.14.

5

What type of access does CVE-2026-3473 allow an attacker?

CVE-2026-3473 allows an authenticated user to access and download files belonging to other users or teams through crafted Boards API requests.

Company

Resources

Contact

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