CVE-2026-12539: Docker Sandboxes ICMP egress restriction bypass after daemon restart
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
For sandbox networks, block ICMP egress after Docker daemon restart using an external control (e.g., firewall/ACL) that is re-enforced on restart, since the ICMP egress authorizer is applied only at network-creation time and is not re-applied when networks are rebuilt from disk.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-12539?
CVE-2026-12539 has a medium severity rating of 5.7 on the CVSS scale.
What is CVE-2026-12539 about?
CVE-2026-12539 involves a bypass of ICMP egress restrictions in Docker Sandboxes after a daemon restart.
How do I fix CVE-2026-12539?
To mitigate CVE-2026-12539, ensure that Docker Sandboxes are configured to enforce ICMP egress restrictions after the Docker daemon restarts.
What software is affected by CVE-2026-12539?
CVE-2026-12539 affects the Docker Engine and Docker Sandboxes.
What are the potential risks associated with CVE-2026-12539?
The risks of CVE-2026-12539 include unauthorized ICMP traffic being forwarded from sandboxed workloads to arbitrary hosts.