CVE-2026-55887 MCP Gateway 0.21.00.42.2: Unmarshaled OCI Label Bypass Privilege Escalation
CVE-2026-55887 Published on September 15, 2026
MCP Gateway: Argument injection via OCI image label YAML in Docker MCP Gateway
MCP Gateway allows easy and secure running and deployment of MCP servers. From 0.21.0 until 0.42.2, Docker MCP Gateway YAML-unmarshalled the attacker-controlled io.docker.server.metadata OCI image label into the broad catalog.Server structure for direct docker:// references and catalog snapshot imports in pkg/oci/self_contained.go and pkg/workingset/workingset.go. Runtime-shaping fields including Volumes, User, and ExtraHosts were then appended to the docker run argument vector without an origin allowlist, allowing a malicious image author to request host filesystem or Docker socket mounts and UID 0 execution when a victim selected or pulled the image. This container-creation-time boundary bypass can execute arbitrary code on the host and is not prevented by no-new-privileges because no in-container privilege escalation is required. This issue is fixed in version 0.42.2.
Vulnerability Analysis
CVE-2026-55887 can be exploited with local system access. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
What is an Argument Injection Vulnerability?
The software constructs a string for a command to executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.
CVE-2026-55887 has been classified to as an Argument Injection vulnerability or weakness.