# CVE-2026-12039: Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution

> CVE-2026-12039: Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution. CVSS 5.7 (CVSS 4.0).

Canonical: https://rewindex.com/cve/CVE-2026-12039
Last updated: 2026-08-13T14:16:53Z

- Published: 2026-06-18 13:48 UTC · Updated: 2026-08-13 14:16 UTC · Assigner: Docker
- CVSS: 5.7 (CVSS 4.0) · Severity: Medium
- EPSS: 0.10%, 1th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-923

## Description

Docker Sandboxes (sbx) enforces an HTTP/S-only egress allowlist but does not apply it to DNS resolution: the per-network embedded DNS server forwards any queried name to the host resolver whenever the network is internet-connected, without consulting the policy. A workload inside a sandbox, which the threat model treats as untrusted, can therefore encode data into DNS labels for an attacker-controlled domain and exfiltrate it through a DNS covert channel, bypassing the configured allowlist.

## Affected vendors and products

- Docker: Docker Sandboxes

## Tracked companies

- [Docker](https://rewindex.com/company/docker.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-12039)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-12039)
- [https://docs.docker.com/ai/sandboxes/](https://docs.docker.com/ai/sandboxes/)
- [https://github.com/docker/sbx-releases/releases/tag/v0.33.0](https://github.com/docker/sbx-releases/releases/tag/v0.33.0)

---

_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


---
Canonical: https://rewindex.com/cve/CVE-2026-12039 · Markdown: https://rewindex.com/cve/CVE-2026-12039.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-12039 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T04:06:43.119Z