CVE-2026-6406: 
Docker Desktop vulnerability analysis and mitigation

CVE-2026-6406 is a local privilege escalation vulnerability in Docker Desktop that allows a local attacker to bypass Enhanced Container Isolation (ECI) restrictions by exploiting the --use-api-socket CLI flag. The flaw affects Docker Desktop versions 4.41.0 through 4.58.x (fixed in 4.59.0). It was reported to Docker on January 9, 2026, and publicly disclosed on April 23, 2026, via a coordinated ZDI advisory. The vulnerability carries a CVSS v3.1 base score of 8.8 (High) and a CVSS v4.0 base score of 8.8 (High) (ZDI Advisory, ENISA EUVD).

The root cause is Incorrect Authorization (CWE-863) in the Docker Desktop API proxy's ECI enforcement logic. When ECI is enabled, the proxy denies Docker socket mounts from containers by inspecting the HostConfig.Binds field — but the --use-api-socket CLI flag routes the socket mount through HostConfig.Mounts instead, which the proxy does not inspect. This allows the mount to pass unchecked, granting the container full access to the Docker Engine socket. An attacker must have the ability to run Docker CLI commands on the host (low-privileged local access) but does not require any additional configuration or user interaction to exploit the flaw (ZDI Advisory, ENISA EUVD).

Successful exploitation allows a local user to escape ECI restrictions and gain full access to the Docker Engine socket with host-level privileges. This enables the attacker to control the Docker daemon, spawn privileged containers, and access any container registry authentication credentials cached by the host user. The changed scope (S:C in CVSS) reflects that the impact extends beyond the container boundary to the host system, with high confidentiality, integrity, and availability impact (ZDI Advisory, ENISA EUVD).

1. Prerequisite: Obtain local access to a system running Docker Desktop 4.41.0–4.58.x with Enhanced Container Isolation (ECI) enabled, and have permission to execute Docker CLI commands.
2. Identify ECI enforcement gap: Recognize that ECI blocks Docker socket mounts via HostConfig.Binds but does not inspect HostConfig.Mounts.
3. Invoke --use-api-socket flag: Run a Docker CLI command using the --use-api-socket flag to start a container. This flag causes the Docker CLI to add the Docker Engine socket (/var/run/docker.sock or equivalent) as a mount via HostConfig.Mounts, bypassing ECI inspection.
4. Access Docker Engine socket: From within the container, interact with the mounted Docker Engine socket to issue privileged Docker API calls — creating new containers, modifying existing ones, or reading host filesystem data.
5. Harvest credentials: Access cached container registry authentication credentials stored by the host user (e.g., from ~/.docker/config.json or the Docker credential store) via the socket connection.
6. Escalate privileges: Use Docker daemon access to launch a privileged container with host filesystem mounts, achieving full host compromise (ZDI Advisory, ENISA EUVD).

• Process/CLI: Docker CLI invocations containing the --use-api-socket flag on systems where ECI is enabled; audit logs showing unexpected container creation with socket mounts.
• File System: Unexpected access to or reads from the Docker Engine socket file (/var/run/docker.sock or platform equivalent) from within a container context; unusual modifications to ~/.docker/config.json.
• Logs: Docker Desktop API proxy logs showing container start requests with HostConfig.Mounts entries referencing the Docker socket that were not blocked by ECI; Docker daemon logs showing API calls originating from within a container.
• Network: Outbound connections to container registries from unexpected processes or containers, potentially indicating credential harvesting and unauthorized image pulls.

The primary remediation is to update Docker Desktop to version 4.59.0 or later, which contains the fix for this vulnerability (ZDI Advisory, Docker Release Notes). As interim workarounds: avoid using the --use-api-socket flag in environments where ECI is relied upon for security isolation, and restrict which users have permission to execute Docker CLI commands on sensitive systems. Organizations should also audit admin-settings configurations to ensure ECI socket mount policies are correctly enforced after upgrading.

The vulnerability was discovered by Nitesh Surana of Trend Research and disclosed through the Zero Day Initiative, which published the advisory on April 23, 2026 (ZDI Advisory). Security aggregators including Tenable (Nessus plugin 311262), VulDB, and ENISA's EUVD catalogued the issue shortly after disclosure. A blog post from SystemTek characterized the flaw as a "dangerous function" exposure in Docker Desktop's ECI, and the vulnerability received coverage from several CVE tracking and threat intelligence platforms. Social media activity on Bluesky and CVE-tracking bots noted the disclosure, though overall community reaction has been measured given the local-only attack vector and low EPSS score.