# CVE-2026-40196: HomeBox has Unauthorized API Access via Retained defaultGroup ID After Group Access Revocation

> Attackers with revoked group access can bypass API controls to read and modify group data due to retained default group IDs.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** No
- **Published:** 17 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-6pvm-v73p-p6m9

## What is CVE-2026-40196?

CVE-2026-40196 is a high-severity missing authorization vulnerability in sysadminsmedia homebox, published on 17 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

HomeBox is a home inventory and organization system. Versions prior to 0.25.0 contain a vulnerability where the defaultGroup ID remained permanently assigned to a user after being invited to a group, even after their access to that group was revoked. While the web interface correctly enforced the access revocation and prevented the user from viewing or modifying the group's contents, the API did not. Because the original group ID persisted as the user's defaultGroup, and this value was not properly validated when the X-Tenant header was omitted, the user could still perform full CRUD operations on the group's collections through the API, bypassing the intended access controls. This issue has been fixed in version 0.25.0.

Weakness: CWE-708 (Incorrect Ownership Assignment)

## Which versions are affected by CVE-2026-40196?

It affects 1 product.


Products: Sysadminsmedia Homebox.

## How do I fix CVE-2026-40196?

No fix has been published for CVE-2026-40196 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-40196 being exploited?

There is no known exploitation of CVE-2026-40196 in the wild and no public exploit code.

## Other vulnerabilities in sysadminsmedia homebox

- [CVE-2026-27981](https://insights.sbomify.com/CVE-2026-27981/): HomeBox has an Auth Rate Limit Bypass via IP Spoofing (high 7.4)
- [CVE-2026-27600](https://insights.sbomify.com/CVE-2026-27600/): HomeBox affected by Blind SSRF (medium 5.0)
- [CVE-2026-26272](https://insights.sbomify.com/CVE-2026-26272/): HomeBox affected by Stored XSS via HTML/SVG Attachment Upload (medium 4.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40196 and fix it if it is affected.

What it is: CVE-2026-40196 is a high-severity missing authorization vulnerability in sysadminsmedia homebox, published on 17 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-2026-40196 in the wild and no public exploit code.

Affected product: sysadminsmedia homebox. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-40196/ (Markdown: https://insights.sbomify.com/CVE-2026-40196/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40196
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40196
- OSV: https://osv.dev/vulnerability/CVE-2026-40196

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40196/
Summaries are generated and may contain mistakes; the official description above is the record.