CVE-2026-12039: CWE-923: Improper Restriction of Communication Channel to Intended Endpoints in Docker Docker Sandboxes
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.
AI Analysis
Technical Summary
Docker Sandboxes (version 0.13.0) enforce an HTTP/S-only egress allowlist but fail to restrict DNS resolution traffic. The embedded per-network DNS server forwards any queried DNS name to the host resolver when the network is internet-connected, bypassing the allowlist policy. This allows an untrusted workload inside a sandbox to encode data into DNS labels for attacker-controlled domains and exfiltrate data covertly via DNS queries. This is classified as CWE-923: Improper Restriction of Communication Channel to Intended Endpoints.
Potential Impact
An attacker controlling a workload inside a Docker Sandbox can bypass the configured HTTP/S egress allowlist by using DNS queries to exfiltrate data covertly. This can lead to unauthorized data leakage from the sandbox environment. The vulnerability does not affect other communication channels and requires local privileges to run workloads inside the sandbox.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, restrict or monitor DNS traffic from sandboxed workloads where possible to detect anomalous DNS queries. Consider network segmentation or egress filtering at the network perimeter to limit DNS exfiltration risks.
CVE-2026-12039: CWE-923: Improper Restriction of Communication Channel to Intended Endpoints in Docker Docker Sandboxes
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.
CVSS v4.0
Score 5.7medium
Affected software
pkg:github/docker/sbx-releasesRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Docker Sandboxes (version 0.13.0) enforce an HTTP/S-only egress allowlist but fail to restrict DNS resolution traffic. The embedded per-network DNS server forwards any queried DNS name to the host resolver when the network is internet-connected, bypassing the allowlist policy. This allows an untrusted workload inside a sandbox to encode data into DNS labels for attacker-controlled domains and exfiltrate data covertly via DNS queries. This is classified as CWE-923: Improper Restriction of Communication Channel to Intended Endpoints.
Potential Impact
An attacker controlling a workload inside a Docker Sandbox can bypass the configured HTTP/S egress allowlist by using DNS queries to exfiltrate data covertly. This can lead to unauthorized data leakage from the sandbox environment. The vulnerability does not affect other communication channels and requires local privileges to run workloads inside the sandbox.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, restrict or monitor DNS traffic from sandboxed workloads where possible to detect anomalous DNS queries. Consider network segmentation or egress filtering at the network perimeter to limit DNS exfiltration risks.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Docker
- Date Reserved
- 2026-06-11T19:23:44.967Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a33ff00f198dc38c1f0d3c9
Added to database: 6/18/2026, 2:21:52 PM
Last enriched: 6/18/2026, 2:35:34 PM
Last updated: 6/18/2026, 5:26:45 PM
Views: 5
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