Vulnerability · Published Apr 3, 2026 · Assigned by Mattermost
CVE-2026-28736Focalboard IDOR in file content endpoint allows cross-user file access (unsupported product, no fix)
Medium 4.3
In plain English
A medium-severity authorization bypass via user-controlled key in Focalboard from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 14% of all known vulnerabilities).
Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.2%top 86.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
** 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/focalboard | no fix listed | GHSA-vph7-r229-qxpf |
| Go | github.com/mattermost/focalboard | no fix listed | GO-2026-5670 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Focalboard | 0 – through 8.0 |
Weakness: CWE-639 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N