File Ownership Validation Flaw in Focalboard by Mattermost
CVE-2026-28736

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Focalboard
Vendor
CVE Published:
3 April 2026

What is CVE-2026-28736?

The Focalboard product version 8.0 contains a vulnerability that fails to properly validate file ownership when serving uploaded files. This enables authenticated attackers, who possess knowledge of a victim's specific fileID, to gain unauthorized access to the contents of those files. It should be noted that Focalboard is currently unmaintained, and no official fix will be provided for this security issue.

Affected Version(s)

Focalboard 0 <= 8.0

References

https://github.com/mattermost-community/focalboard
product

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Siam Thanat Hack Company Limited
.