CVE-2026-3473 PUBLISHED

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

Assigner: Mattermost
Reserved: 03.03.2026 Published: 22.05.2026 Updated: 22.05.2026

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

Metrics

CVSS 3.1

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

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

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.6.0 to 11.6.0 (incl.) affected from 11.5.0 to 11.5.3 (incl.) affected from 11.4.0 to 11.4.4 (incl.) affected from 10.11.0 to 10.11.14 (incl.) Version 11.7.0 is unaffected Version 11.6.1 is unaffected Version 11.5.4 is unaffected Version 11.4.5 is unaffected Version 10.11.15 is unaffected

Solutions

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

Credits

eahmed finder

References

MMSA-2026-00620

Problem Types

CWE-639: Authorization Bypass Through User-Controlled Key CWE