src/Composer/Installer/InstallationManager.php
public function disablePlugins()
    {
        foreach ($this->installers as $i => $installer) {
            if (!$installer instanceof PluginInstaller) {
                continue;
            }

            unset($this->installers[$i]);
        }
    }
public function disablePlugins()
    {
        foreach ($this->installers as $i => $installer) {
            if (!$installer instanceof PluginInstaller) {
                continue;
            }

            unset($this->installers[$i]);
        }
    }
Disables plugins.

We prevent any plugins from being instantiated by simply
deactivating the installer for them. This ensure that no third-party
code is ever executed.