{"id":"GHSA-qg2g-g9w3-m5h8","summary":"ToolHive: containerized MCP servers can reach host services via host.docker.internal, enabling lateral movement","details":"## Summary\n\nA containerized MCP server running with the default `network` permission profile (`insecure_allow_all: true`) can reach host-local services via `host.docker.internal`. This includes the ToolHive API itself, other ToolHive-managed MCP server proxies, and any other service listening on the host's localhost. Combined with the unauthenticated ToolHive API and MCP proxy endpoints, this enables a compromised or malicious MCP server to perform lateral movement without any container escape.\n\n## Severity\n\n**High** — This bypasses the container isolation model that is ToolHive's core security value proposition.\n\n## Reproduction\n\nAll tests performed from inside the `filesystem` MCP container (`docker.io/mcp/filesystem:latest`), started with default settings via `thv run filesystem -- /tmp`.\n\n### 1. Container can reach the ToolHive control plane MCP endpoint\n\n```bash\n$ docker exec \u003ccontainer_id\u003e wget -qO- \\\n  --header=\"Content-Type: application/json\" \\\n  --header=\"Accept: application/json\" \\\n  --post-data='{\"jsonrpc\":\"2.0\",\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2025-03-26\",\"capabilities\":{},\"clientInfo\":{\"name\":\"evil-mcp\",\"version\":\"1.0\"}},\"id\":1}' \\\n  http://host.docker.internal:50444/mcp\n```\n\n**Result:** Full MCP handshake succeeds:\n```json\n{\"jsonrpc\":\"2.0\",\"id\":1,\"result\":{\"protocolVersion\":\"2025-03-26\",\"capabilities\":{\"logging\":{},\"tools\":{}},\"serverInfo\":{\"name\":\"toolhive-mcp\",\"version\":\"v0.9.3\"}}}\n```\n\n### 2. Container can connect to another MCP server's proxy and call its tools\n\n```bash\n$ docker exec \u003ccontainer_id\u003e wget -qO- \\\n  --header=\"Content-Type: application/json\" \\\n  --header=\"Accept: application/json\" \\\n  --post-data='{\"jsonrpc\":\"2.0\",\"method\":\"tools/list\",\"params\":{},\"id\":2}' \\\n  http://host.docker.internal:64965/mcp\n```\n\n**Result:** Returns the full tool list of the target MCP server (read_file, write_file, edit_file, move_file, etc.), and tools can be called:\n\n```json\n{\"jsonrpc\":\"2.0\",\"id\":3,\"result\":{\"content\":[{\"text\":\"Allowed directories:\\n/tmp\",\"type\":\"text\"}]}}\n```\n\n### 3. Container can reach other host services\n\n```bash\n# Kubernetes API\n$ docker exec \u003ccontainer_id\u003e wget -qO- --no-check-certificate https://host.docker.internal:6443/version\n{\"major\":\"1\",\"minor\":\"34\",\"gitVersion\":\"v1.34.1\"...}\n\n# Ollama LLM API\n$ docker exec \u003ccontainer_id\u003e wget -qO- http://host.docker.internal:11434/api/tags\n{\"models\":[{\"name\":\"kimi-k2:1t-cloud\"...}]}\n```\n\n## Attack Scenarios\n\n### Scenario 1: Malicious MCP server pivots to privileged native MCP tools\n\nMany users run native (non-containerized) MCP servers like Desktop Commander, terminal servers, or custom tools that have `execute_command`, `write_file`, or `shell` capabilities with full host access. These typically listen on localhost ports. A malicious containerized MCP server can:\n\n1. Port-scan `host.docker.internal` to discover listening services\n2. Attempt MCP handshakes on discovered ports\n3. Call privileged tools (e.g., `execute_command(\"rm -rf /\")` or `write_file(\"/etc/crontab\", \"...\")`)\n\nThis achieves **full host compromise without any container escape vulnerability**.\n\n### Scenario 2: Compromised MCP server manipulates ToolHive itself\n\nVia the unauthenticated ToolHive MCP endpoint on port 50444, a compromised container could potentially:\n\n- List and stop other running MCP servers (denial of service)\n- Start new MCP servers with attacker-controlled images\n- Modify configurations\n\n### Scenario 3: Data exfiltration via cross-MCP-server access\n\nA low-privilege MCP server (e.g., `sequentialthinking` with no file mounts) could reach the `filesystem` server's proxy and call `read_file` to access files it was never authorized to see.\n\n### Scenario 4: LLM model theft / abuse\n\nAs demonstrated, the container can reach Ollama's API and could enumerate models, run inference, or exfiltrate model weights from self-hosted LLMs.\n\n## Root Causes\n\n1. **`insecure_allow_all: true` as default** — permits outbound connections to any destination including `host.docker.internal`\n2. **No authentication on ToolHive API / MCP proxies** — any client that can reach the port can interact fully\n3. **Docker's `host.docker.internal` DNS** — resolves to the host machine, bypassing localhost-only binding assumptions\n\n## Suggested Mitigations\n\n### Short-term\n\n- **Block `host.docker.internal` and `172.17.0.1`** (Docker gateway) in container networking by default, even when `insecure_allow_all` is enabled. These should require explicit opt-in.\n- **Add authentication to MCP proxy endpoints** — even a shared secret or token per session would prevent cross-container lateral movement.\n\n### Medium-term\n\n- **Network policy per container** — ToolHive already has the `permission_profile` infrastructure. Add support for explicit allow-lists rather than just the binary none/all choice.\n- **Isolate container networks** — run each MCP server in its own Docker network with no access to the Docker bridge gateway.\n\n### Long-term\n\n- **Mutual TLS or token-based auth** between ToolHive proxy and containers, so even if network access exists, unauthorized MCP calls are rejected.\n- **Audit logging** — log all MCP tool calls with source identification so lateral movement attempts are visible.\n\n## Environment\n\n- ToolHive v0.9.3 (macOS desktop app, Docker runtime)\n- Docker Desktop for Mac (host.docker.internal enabled by default)\n- Tested with `docker.io/mcp/filesystem:latest`","aliases":["CVE-2026-58197","GO-2026-6526"],"modified":"2026-09-28T17:10:42.435599757Z","published":"2026-09-18T17:16:02Z","database_specific":{"github_reviewed_at":"2026-09-18T17:16:02Z","nvd_published_at":null,"cwe_ids":["CWE-284","CWE-306"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/stacklok/toolhive/security/advisories/GHSA-qg2g-g9w3-m5h8"},{"type":"WEB","url":"https://github.com/stacklok/toolhive-studio/pull/2469"},{"type":"WEB","url":"https://github.com/stacklok/toolhive/pull/5583"},{"type":"WEB","url":"https://github.com/stacklok/toolhive-studio/commit/968182d7f3ee1e55123369e66ad88f82128119b0"},{"type":"WEB","url":"https://github.com/stacklok/toolhive/commit/d8f40cb1599b8bf66657f2dfff15bfbfc236e712"},{"type":"PACKAGE","url":"https://github.com/stacklok/toolhive"},{"type":"WEB","url":"https://github.com/stacklok/toolhive-studio/releases/tag/v0.38.0"},{"type":"WEB","url":"https://github.com/stacklok/toolhive/releases/tag/v0.30.1"}],"affected":[{"package":{"name":"github.com/stacklok/toolhive","ecosystem":"Go","purl":"pkg:golang/github.com/stacklok/toolhive"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.30.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-qg2g-g9w3-m5h8/GHSA-qg2g-g9w3-m5h8.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H"}]}