CVE-2026-12539: docker docker sandboxes Improper Initialization

Vulnerability summary

CVE-2026-12539 is a medium (CVSS 5.7) Improper Initialization vulnerability in docker docker sandboxes. EPSS estimates a 0.14% chance of exploitation in the next 30 days, higher than 2.9% of scored vulnerabilities.

Timeline

1. 18-06-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-665Improper InitializationThe product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.
• CWE-923Improper Restriction of Communication Channel to Intended EndpointsThe product establishes a communication channel to (or from) an endpoint for privileged or protected operations, but it does not properly ensure that it is communicating with the correct endpoint.