# Microsoft eXecution Container (MXC)

By Saurabh Kumar · TIL note, Oct 10, 2026 · Tags: harness, security

Source: https://saurabh-kumar.com/til/1791633600/

[Microsoft eXecution Container (MXC)](https://github.com/microsoft/mxc) is an embeddable SDK for running untrusted commands under OS-enforced policies, not a hosted sandbox service.
- Defaults: Seatbelt on macOS, Bubblewrap on Linux, ProcessContainer on Windows. SDKs for Node, Rust, and .NET.
- Restricts filesystem and network access. macOS hostname allowlists need a caller-managed proxy; not every backend is a VM.
- Useful boundary: sandbox the command where it executes, not just the agent's tool-composition script. Isolation limits damage; it does not make generated output trustworthy.