CVE-2026-28736: Github.com/mattermost/focalboard Focalboard Doesn't Validate File Ownership Vulnerability

MODERATE
Advisory Identifier: GHSA-vph7-r229-qxpf
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CVSS 4.3
CWE-639
Published
Advisory Summary

CVE-2026-28736 is a MODERATE (CVSS 4.3) focalboard doesn't validate file ownership vulnerability (CWE-639: Authorization Bypass Through User-Controlled Key) affecting Github.com/mattermost/focalboard libraries in the Go ecosystem. The issue involves focalboard doesn't validate file ownership when serving uploaded files. Remediation is available in the latest vendor maintenance releases.

CVE-2026-28736 at a Glance

CVE Identifier CVE-2026-28736
GHSA Identifier GHSA-vph7-r229-qxpf
Severity MODERATE
CVSS v3.1 Base Score 4.3
CWE Classification CWE-639: Authorization Bypass Through User-Controlled Key
Affected Product Github.com/mattermost/focalboard
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 4.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-28736

To remediate this vulnerability, upgrade all affected Github.com/mattermost/focalboard dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/mattermost/focalboard fixed: Latest secure release 
Upgrade github.com/mattermost/focalboard to Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/mattermost/focalboard

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-28736, inspect your project dependencies for Github.com/mattermost/focalboard:

inspect dependencies for github.com/mattermost/focalboard

Analyze the terminal output to locate any version of Github.com/mattermost/focalboard in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-639: Authorization Bypass Through User-Controlled Key, where the system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. In Github.com/mattermost/focalboard, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

** 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.

CVE-2026-28736 Affected Github.com/mattermost/focalboard Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
github.com/mattermost/focalboard
golang/github.com/mattermost/focalboard
Go
≤ 7.10.6

References

NVD — CVE-2026-28736 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-28736
Github.com/mattermost/focalboard Source Repository REPOSITORY
https://github.com/mattermost-community/focalboard

Frequently Asked Questions

What is CVE-2026-28736?
CVE-2026-28736 is a security vulnerability in Github.com/mattermost/focalboard involving Focalboard doesn't validate file ownership when serving uploaded files under CWE-639: Authorization Bypass Through User-Controlled Key.
Which Github.com/mattermost/focalboard versions are affected?
Affected versions include releases prior to current release patches across affected packages: github.com/mattermost/focalboard.
What version fixes CVE-2026-28736?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/mattermost/focalboard affected?
Yes, github.com/mattermost/focalboard is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-28736?
CVE-2026-28736 has a CVSS v3.1 base score of 4.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2026-28736?
CVE-2026-28736 is classified under CWE-639: Authorization Bypass Through User-Controlled Key (The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.).
How can I check Go dependencies for CVE-2026-28736?
Run the dependency tree command: 'inspect dependencies for github.com/mattermost/focalboard'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vph7-r229-qxpf",
  "modified" : "2026-04-06T15:08:47Z",
  "published" : "2026-04-03T15:30:31Z",
  "aliases" : [ "CVE-2026-28736" ],
  "summary" : "Focalboard doesn't validate file ownership when serving uploaded files",
  "details" : "** 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/mattermost/focalboard"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "7.10.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-28736"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mattermost-community/focalboard"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-639" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-06T15:08:47Z",
    "nvd_published_at" : "2026-04-03T14:16:29Z"
  }
}