Review reviewHigh

CVE-2026-3473

Mattermost Mattermost, mattermost server

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

CVSS: 7.1
EPSS: 0.15%
CISA KEV: Not listed
Published: 2026.05.22

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.15%

Technical severityCVSS 7.1

Vulnerability overview

Affected product and versions

Product: Mattermost Mattermost, mattermost server
Affected versions: >= 11.6.0 <= 11.6.0, >= 11.5.0 <= 11.5.3, >= 11.4.0 <= 11.4.4, >= 10.11.0 <= 10.11.14, >= 10.11.0 < 10.11.15, >= 11.4.0 < 11.4.5, >= 11.5.0 < 11.5.4, >= 11.6.0 < 11.6.1
Fixed versions: 10.11.15, 11.4.5, 11.5.4, 11.6.1

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that Mattermost Mattermost, mattermost server and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
CWE: CWE-639