launch-as

Launch-as is currently used in agent-win-sandbox to create a least-privilege session for a coding agent like Claude Code or GitHub Copilot CLI.

The current stable version is still v3.2.0. Browse the stable v3.2.0 version. It creates the session via CreateProcessWithLogonW from the current user. However, this has some security implications due to derived logon session tokens:

• Session user will be able to see and interact with the regular user's desktop.
• For regular-user processes that retain the normal logon-SID default-DACL ACE, the session user can obtain PROCESS_VM_READ and PROCESS_TERMINATE, allowing memory reads and termination. Protected processes or processes with custom DACLs may not be accessible.

1.0.0-preview · Windows x64 · console programs only

launch-as starts a console program as an enrolled local standard account through the launch-as-broker Windows service. The client never accepts, reads, stores, or transmits the account password. The broker creates an independent logon session, so the child does not inherit the caller's logon SID or its default access to the caller's processes.

This is a general-purpose alternate-account launcher: its authorised caller can choose an enrolled account and any absolute executable. It is blast-radius reduction, not a sandbox: it does not protect against a local administrator or kernel-level attacker. GUI applications are out of scope for this preview.

Install the binary package

Extract launch-as-v1.0.0-preview-win64.zip and run the bundled setup script from its extracted directory. It elevates when needed, installs or updates the demand-start service, and can enroll a default account. The user who runs install becomes the broker's authorised caller.

.\Setup-LaunchAs.ps1

The package contains launch-as.exe, launch-as-admin.exe, launch-as-broker.exe, launch-as-conhost.exe, this README, the setup script, and the license. Keep launch-as-admin.exe, launch-as-broker.exe, and launch-as-conhost.exe together while installing; setup copies the broker and console host to %ProgramFiles%\launch-as with protected permissions.

Setup

For automation or individual elevated administration operations, use launch-as-admin.exe. Run these commands from the extracted package directory (or out\build\Release after a source build):

.\launch-as-admin.exe install
.\launch-as-admin.exe enroll LaunchAsUser

install, enroll, unenroll, and uninstall require elevation. install stops active broker sessions before updating the service. enroll creates a missing non-administrative local account, or takes over an existing one by setting a broker-owned password. It prompts before changing an account; --force is the explicit non-interactive override.

The broker creates a password for each launch, uses it only to log on, then wipes it. An enrolled account runs one session at a time; a second launch fails immediately. unenroll forgets the enrollment and disables the account, but does not delete the Windows account.

.\launch-as-admin.exe list
.\launch-as-admin.exe unenroll LaunchAsUser
.\launch-as-admin.exe uninstall

Launch

From a normal terminal, launch an enrolled account in the current pane:

.\launch-as.exe `
    --user LaunchAsUser `
    --working-directory C:\dev\project `
    -- C:\Windows\System32\cmd.exe /d /k

run is an optional spelling of the same command. The client starts the demand-start broker, creates the terminal data pipes, and returns the target program's exit code. The broker owns the temporary launch password and kills the console job when the client control connection closes.

Build and test

The source build requires Visual Studio/MSVC, a Windows SDK, CMake 3.25+, PowerShell, ninja, and clang-format. Run build.ps1 from the repository root; it initializes the MSVC environment when needed and builds the Ninja Multi-Config Release target by default.

.\build.ps1
.\build.ps1 -Configuration Debug
.\build.ps1 -RunTests

-RunTests runs every non-elevated CTest test. The installed-service acceptance checks remain explicit because they require elevation and an enrolled account:

.\tests\Invoke-BrokerConsoleAcceptanceTest.ps1 -Account LaunchAsUser -ExpectedExitCode 37
.\tests\Invoke-BrokerProbeAcceptanceTest.ps1 -Account LaunchAsUser

The probe confirms a distinct logon SID, no interactive windows, and denied VM_READ and TERMINATE access to the caller's process. These are blast-radius controls, not protection from a local administrator or kernel-level attacker.

Design

launch-as-broker-spec.md is the Phase 1 implementation specification. The interactive GUI adapter is deliberately deferred to Phase 2; Phase 1 provides console (ConPTY) launches only.

License

launch-as is licensed under the GNU General Public License version 3 only. Source for this preview is available at https://github.com/fmuecke/launch-as/tree/v1.0.0-preview.