CVE-2026-3473

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

CVSS 5.9 MEDIUMEPSS 0.1%CWE-639

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 5.9EPSS 0.1%KEV nãoPoC —Nuclei —Metasploit —Patch referenciado

Lifecycle

22 May 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N

Affected products

Mattermost · Mattermost

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References

https://mattermost.com/security-updates