Docker Sandbox DNS Exfil via Resolver Bypass
CVE-2026-12039 Published on June 18, 2026
Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution
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.
Weakness Type
Improper Restriction of Communication Channel to Intended Endpoints
The software establishes a communication channel to (or from) an endpoint for privileged or protected operations, but it does not properly ensure that it is communicating with the correct endpoint.
Products Associated with CVE-2026-12039
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Affected Versions
Docker Sandboxes:- Version 0.13.0 and below 0.33.0 is affected.