CVE-2026-12039

Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution

Published Jun 18, 2026 CVSS 4.0 · 5.7 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:docker:sandboxes:*:*:*:*:*:*:*:* cpe:2.3:a:docker:docker_sandboxes:*:*:*:*:*:*:*:*
Vendors & Products Docker sandboxes
Type Values Removed Values Added
First Time appeared Docker sandboxes
CPEs cpe:2.3:a:docker:sandboxes:*:*:*:*:*:*:*:*
Vendors & Products Docker sandboxes
Type Values Removed Values Added
First Time appeared Docker
Docker docker Sandboxes
Vendors & Products Docker
Docker docker Sandboxes
Type Values Removed Values Added
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.
Title Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution
Weaknesses CWE-923
References
Metrics cvssV4_0

{'score': 5.7, 'vector': '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'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Docker
Published
Updated
Aug 13, 2026, 1:33 PM
Reserved
Jun 11, 2026, 7:23 PM
Status
Awaiting Analysis
Published
Jun 18, 2026, 2:17 PM
Modified
Oct 26, 2026, 11:10 AM