What is CVE-2026-28736?

CVE-2026-28736 is a medium-severity vulnerability in Mattermost Focalboard, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2026-04-03.

How severe is CVE-2026-28736?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Auth bypass in Mattermost Focalboard

CVE-2026-28736

** UNSUPPORTED WHEN ASSIGNED ** Focalboard version 8.0 fails to validate file ownership when serving uploaded files. This allows an authenticated attacker who knows a victim's fileID to read the content of the file. NOTE: Focalboard as a s…

Vulnerability class: IDOR (Insecure Direct Object Reference)

EPSS: 0.000 (1.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

Affected products

Mattermost Focalboard — versions 8.0.0, 0

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

Focalboard Repository (Unmaintained) (Product, product)

Frequently asked questions

What is CVE-2026-28736?: CVE-2026-28736 is a medium-severity vulnerability in Mattermost Focalboard, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 4.3/10. Published 2026-04-03.
How severe is CVE-2026-28736?: Medium severity. CVSS v3 base score is 4.3 out of 10.