# CVE-2026-123784: Fluxbox through 1.3.7 OS Command Injection via Style Background Values


- **Severity:** High 8.5 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 6 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-123784, GHSA-c5cr-c2wq-j45j, UBUNTU-CVE-2026-123784

## What is CVE-2026-123784?

CVE-2026-123784 is a high-severity vulnerability in fluxbox, published on 6 Nov 2026. 

### Official description

Fluxbox through 1.3.7 contains an OS command injection vulnerability in RootTheme::reconfigTheme() that allows attackers to execute commands via crafted style background values. Attackers can embed shell metacharacters in background pixmap paths, random directories, or gradient texture text, which are concatenated unescaped into an fbsetbg command run via $SHELL -c when the style loads.

Weakness: CWE-78 (Improper Neutralization of Special Elements used in an OS Command)

## Which versions are affected by CVE-2026-123784?


## How do I fix CVE-2026-123784?

No fix has been published for CVE-2026-123784 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-123784 being exploited?

There is no known exploitation of CVE-2026-123784 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123784 and fix it if it is affected.

What it is: CVE-2026-123784 is a high-severity vulnerability in fluxbox, published on 6 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-123784 in the wild and no public exploit code.

Affected product: fluxbox. 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-2026-123784/ (Markdown: https://insights.sbomify.com/CVE-2026-123784/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123784
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123784
- OSV: https://osv.dev/vulnerability/CVE-2026-123784

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123784/
Summaries are generated and may contain mistakes; the official description above is the record.