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

Status: published. Published: 2026-11-06. Updated: 2026-11-11.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/fluxbox/fluxbox/pull/89
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/fluxbox/fluxbox/commit/270bfbc28573037c9b8458488d193b219e33889f

## Affected products and versions

- fluxbox / fluxbox (fluxbox/fluxbox): ≥ 0; ≤ 1.3.7 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.5 (high); 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; source: CNA: VulnCheck

- CVSS 3.1: 7.8 (high); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: CNA: VulnCheck

- CVSS 4.0: 8.5 (high); 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 7.8 (high); CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.71% as of 2026-11-10; percentile 53.78%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-78

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/fluxbox/fluxbox/pull/89 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/fluxbox/fluxbox (CNA: VulnCheck; product)

- https://github.com/fluxbox/fluxbox/commit/270bfbc28573037c9b8458488d193b219e33889f (CNA: VulnCheck; patch)

- https://github.com/fluxbox/fluxbox/blob/Release-1_3_7/src/RootTheme.cc#L192-L264 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/fluxbox-through-1.3.7-os-command-injection-via-style-background-values (CNA: VulnCheck; third-party-advisory)

- https://github.com/fluxbox/fluxbox (disclosure@vulncheck.com)

- https://github.com/fluxbox/fluxbox/blob/Release-1_3_7/src/RootTheme.cc#L192-L264 (disclosure@vulncheck.com)

- https://github.com/fluxbox/fluxbox/commit/270bfbc28573037c9b8458488d193b219e33889f (disclosure@vulncheck.com)

- https://github.com/fluxbox/fluxbox/pull/89 (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/fluxbox-through-1.3.7-os-command-injection-via-style-background-values (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-123784; retrieved 2026-11-11; source updated 2026-11-11

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123784; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-123784; retrieved 2026-11-11; source updated Not reported

Revision: 4491464694829dd9d137c53274461f054c26c7abd6d2446f7c840de96892f056

Canonical: https://y2.dev/cve/CVE-2026-123784

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