CVE-2026-12039 Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution
Untrusted workloads in Docker Sandboxes can bypass network egress allowlists and exfiltrate data via DNS covert channels due to unfiltered DNS resolution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-12039?
CVE-2026-12039 is a medium-severity vulnerability in Docker Sandboxes, published on 18 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-923
Which versions are affected by CVE-2026-12039?
How do I fix CVE-2026-12039?
No fix has been published for CVE-2026-12039 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-12039 being exploited?
There is no known exploitation of CVE-2026-12039 in the wild and no public exploit code.
Sources
Also known as GHSA-4crj-qc6g-g3xj.