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MCPX_DOCKER_SNAP_APPARMOR

Severity: warn Domain: Docker

What happened​

mcpproxy's security scanner sandbox launches the upstream stdio server inside a Docker container with --security-opt no-new-privileges and a pinned AppArmor profile. On Ubuntu's snap-installed Docker, AppArmor's profile transition combined with no-new-privileges causes every command in the container to fail with operation not permitted — the scanner can't run.

This is a known incompatibility between snap Docker's AppArmor confinement and the security flags mcpproxy needs for the scanner. Other (non-scanner) Docker isolation works fine.

How to fix​

You have four options:

sudo snap remove docker
# Then install Docker Desktop, Colima, or rootless Docker
# https://docs.docker.com/engine/install/ubuntu/

2. Use native sandbox isolation instead of Docker (no Docker daemon needed)​

If the real goal is to confine stdio servers on a snap-docker host, switch the isolation mode to sandbox. Servers are confined natively with a Linux Landlock filesystem allowlist + setrlimit (kernel 5.13+), which is unaffected by the snap-docker/AppArmor conflict because it needs no Docker and no user namespaces:

{ "docker_isolation": { "mode": "sandbox" } }

Trade-off: the Docker-based scanner plugins cannot run under sandbox, so they are skipped and the affected server's security_scan.status becomes degraded (the always-on in-process tpa-descriptions scanner still runs). This is MCP-34.4 / D3 option (b) — clean, surfaced degradation. See Security Isolation → Scanner behaviour.

3. Disable the scanner for this server (dry-run shown by default)​

The error panel includes a Disable scanner for this server fix-step. The CLI equivalent:

mcpproxy upstream patch <server-name> --no-scanner --dry-run

Drop --dry-run to apply. The server will still run with isolation, but without TPA pre-flight scanning.

4. Run mcpproxy without isolation for that server​

If you trust the upstream and don't need isolation:

{ "isolation": { "enabled": false } }

Background​

See scanner snap-docker AppArmor incompatibility for the upstream tracking issue.