CVE-2026-28736 PUBLISHED

Focalboard IDOR in file content endpoint allows cross-user file access (unsupported product, no fix)

Assigner: Mattermost
Reserved: 03.04.2026 Published: 03.04.2026 Updated: 03.04.2026

** 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 standalone product is not maintained and no fix will be issued.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
CVSS Score: 4.3

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

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Focalboard
Versions	Default: unaffected affected from 0 to 8.0 (incl.)

Credits

Siam Thanat Hack Company Limited finder

References

Focalboard Repository (Unmaintained)

Problem Types

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