# 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.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Apr 2026
- **Updated:** 3 Apr 2026
- **Also known as:** GHSA-vph7-r229-qxpf, GO-2026-5670

## 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 (Authorization Bypass Through User-Controlled Key)

## 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 | Ecosystem | 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: Mattermost Focalboard.

## How do I fix CVE-2026-28736?

Product is end of life, replace it.

## 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

- [CVE-2026-25773](https://insights.sbomify.com/CVE-2026-25773/): Focalboard doesn't sanitize category IDs before incorporating them into dynamic SQL statements (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28736 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-28736 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/mattermost/focalboard (Go): affected all versions; no fix listed
- github.com/mattermost/focalboard (Go): affected all versions up to 7.10.6; no fix listed
- github.com/mattermost/focalboard (Go): affected all versions up to 7.10.6; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-28736/ (Markdown: https://insights.sbomify.com/CVE-2026-28736/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28736
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28736
- OSV: https://osv.dev/vulnerability/CVE-2026-28736

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28736/
Summaries are generated and may contain mistakes; the official description above is the record.