CVE-2026-3473

Improper file ownership validation in the Boards API allows unauthorised file access

State: Published
Severity: 5.9 Medium
Published: May 22, 2026
Updated: May 22, 2026
Reserved: Mar 3, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	5.9 Medium	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N	Mattermost

Weaknesses

CWE-639 Authorization Bypass Through User-Controlled Key

Affected Products

Product	Versions
MattermostMattermost	11.6.0 through 11.6.0Affected 11.5.0 through 11.5.3Affected 11.4.0 through 11.4.4Affected 10.11.0 through 10.11.14Affected 11.7.0Not affected 11.6.1Not affected 11.5.4Not affected 11.4.5Not affected 10.11.15Not affected

References

MMSA-2026-00620vendor-advisory

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