CVE-2026-28736 Focalboard IDOR in file content endpoint allows cross-user file access (unsupported product, no fix)
An authenticated attacker can read other users' files by guessing file IDs due to missing ownership validation in Focalboard.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-28736?
CVE-2026-28736 is a medium-severity missing authorization vulnerability in Mattermost Focalboard, published on 3 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Weakness: CWE-639
Which versions are affected by CVE-2026-28736?
3 open source packages ship an affected version, including github.com/mattermost/focalboard. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/mattermost/focalboard Go | All versions | None |
github.com/mattermost/focalboard Go | All versions to 7.10.6 | None |
github.com/mattermost/focalboard Go | All versions to 7.10.6 | None |
Products include Mattermost Focalboard.
How do I fix CVE-2026-28736?
Product is end of life, replace it.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-28736 being exploited?
There is no known exploitation of CVE-2026-28736 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Focalboard
Sources
Also known as GHSA-vph7-r229-qxpf, GO-2026-5670.