CVE-2026-28736: UNSUPPORTED WHEN ASSIGNED Focalboard version 8.0 fails to validate file ownership when serving uploaded

Routine

MEDIUM 4.3DOWNGRADE

CVE-2026-28736 is a medium-severity flaw (CVSS 4.3) affecting focalboard. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

** 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.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-639
Published	2026-04-03
Last modified	2026-10-23

Publisher (CNA): Mattermost, Inc. · Vendor: mattermost

Last updated 2026-10-23 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-03 14:16 UTCPublished CVE record published
2026-10-23 22:10 UTCUpdated Record last modified

mattermost focalboard DOWNGRADE

Affected: 8.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0.0

1. Check installed version

apt-cache policy focalboard || rpm -q focalboard || focalboard --version

2. No fixed release: DOWNGRADE to a release before 8.0.0 (Debian / Ubuntu)

apt-cache madison focalboard sudo apt install focalboard=<VERSION_BEFORE_8.0.0> sudo apt-mark hold focalboard

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list focalboard sudo dnf downgrade focalboard-<VERSION_BEFORE_8.0.0> sudo dnf versionlock add focalboard

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-28736?

focalboard: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-28736 being exploited?

CVE-2026-28736 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-28736 affect?

CVE-2026-28736 affects focalboard. Severity is medium (CVSS 4.3). ** 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 st

How urgent is CVE-2026-28736?

Priority 20/100. No elevated risk signals yet.

References

← Back to latest CVEs

CVE-2026-28736: ** UNSUPPORTED WHEN ASSIGNED ** Focalboard version 8.0 fails to validate file ownership when serving uploaded