CVE-2026-12039

Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution

State: Published
Severity: 5.7 Medium
Published: Jun 18, 2026
Updated: Aug 13, 2026
Reserved: Jun 11, 2026

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.

Scores

CVSS	Score	Vector	Source
4.0	5.7 Medium	CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N	Docker

Weaknesses

CWE-923 Improper Restriction of Communication Channel to Intended Endpoints

Affected Products

Product	Versions
Docker SandboxesDocker	0.13.0 to before 0.33.0Affected

References

https://docs.docker.com/ai/sandboxes/product
https://github.com/docker/sbx-releases/releases/tag/v0.33.0release-notes

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