CVE-2026-12039: Docker Sandboxes

Medium severity, CVSS 5.7. EPSS: 0.1% chance of exploitation in the next 30 days.

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 products

• Docker Docker Sandboxes: from 0.13.0, before 0.33.0 (fixed in 0.33.0)

Published 2026-06-18. Last modified 2026-08-13.