Improper Scope Validation in the `open` Endpoint of `tauri-plugin-shell`

Impact

The Tauri shell plugin exposes functionality to execute code and open programs on the system. The open endpoint of this plugin is designed to allow open functionality with the system opener (e.g. xdg-open on Linux). This was meant to be restricted to a reasonable number of protocols like https or mailto by default.

This default restriction was not functional due to improper validation of the allowed protocols, allowing for potentially dangerous protocols like file://, smb://, or nfs:// and others to be opened by the system registered protocol handler.

By passing untrusted user input to the open endpoint these potentially dangerous protocols can be abused to gain remote code execution on the system. This either requires direct exposure of the endpoint to application users or code execution in the frontend of a Tauri application.

You are not affected if you have explicitly configured a validation regex or manually set the open endpoint to true in the plugin configuration.

Technically the scope was never a limitation for the rust side as it is not seen as an enforceable security boundary but we decided to mark the rust crate as affected since the plugin does not need to be a frontend dependency to be exposed.

Patches

The issue has been patched in the 2.2.1 version of the plugin. The plugin now differentiates between an unset scope and an explicit validation disable for the open endpoint.

Workarounds

A way to prevent arbitrary protocols would be setting the shell plugin configuration value open to true.

tauri.conf.json

"plugins": {
    "shell": {
          "open": true
     },
}

The above will only allow mailto, http and https links to be opened.

If the open endpoint should not be allowed at all there are two possible workarounds.

• Defining a non matching regex like tauri^ in the plugin configuration
• Removing shell:default and all instances of shell:allow-open from the capabilities

Alternatively we recommend usage of the opener plugin, as the shell plugin deprecated the open endpoint previously.

References

PoC

This is a windows specific proof of concept.

1. Use create-tauri-app to make a new Tauri app.
2. Run tauri add shell to add the shell plugin.
3. Execute await window.__TAURI_INTERNALS__.invoke("plugin:shell|open", {path: "file:///c:/windows/system32/calc.exe"}); in the developer console.
4. Observe the calculator being executed