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MEDIUM severity

CVE-2026-28736 — focalboard

MEDIUM

CVE-2026-28736 is a medium-severity (CVSS 4.3) CWE-639 vulnerability in github.com/mattermost/focalboard. The records list no fixed version yet; check the vendor advisory below and apply the mitigations in the meantime.

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

Also known asGHSA-vph7-r229-qxpfGO-2026-5670
Published
Updated
Affected
1 pkg
Patched
See advisory
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28736.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk
0.00%0.26%0.51%0.77%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/mattermost/focalboard

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

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

1 total
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/mattermost/focalboardall versionsNo fix

Affected Products

1 product · 1 configurations
Application
focalboardmattermost
1 version
8.0.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/focalboard, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Remediation status

    The records we use list no patched version of github.com/mattermost/focalboard for CVE-2026-28736. Check the maintainer's advisory, and where your build allows, override or pin the dependency away from the vulnerable range.

  3. Mitigate without a patch

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

** 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.
O3 Security · Impact-Aware SCA

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CVE-2026-28736: focalboard (Medium 4.3)