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

> Attackers in Docker Sandboxes can bypass ICMP egress restrictions after daemon restarts to perform reconnaissance and exfiltrate data via ICMP covert channels.

- **Severity:** Medium 5.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Jun 2026
- **Updated:** 13 Aug 2026
- **Also known as:** GHSA-x6hr-f96v-hhgg

## What is CVE-2026-12539?

CVE-2026-12539 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) 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.

Weakness: CWE-923 (Improper Restriction of Communication Channel to Intended Endpoints), CWE-665 (Improper Initialization)

## Which versions are affected by CVE-2026-12539?


## How do I fix CVE-2026-12539?

No fix has been published for CVE-2026-12539 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-12539 being exploited?

There is no known exploitation of CVE-2026-12539 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12539 and fix it if it is affected.

What it is: CVE-2026-12539 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.
Exploitation: There is no known exploitation of CVE-2026-12539 in the wild and no public exploit code.

Affected product: Docker Sandboxes. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-12539/ (Markdown: https://insights.sbomify.com/CVE-2026-12539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12539
- OSV: https://osv.dev/vulnerability/CVE-2026-12539

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12539/
Summaries are generated and may contain mistakes; the official description above is the record.