Merge remote-tracking branch 'curry684/issue-5119'

src/Composer/Console/Application.php

@@ -133,6 +133,19 @@ class Application extends BaseApplication
                 $input->setInteractive(false);
             }
 
+            if (!Platform::isWindows()) {
+                if (function_exists('posix_getuid') && posix_getuid() === 0) {
+                    $io->writeError('<warning>Running composer as root is highly discouraged as packages, plugins and scripts cannot always be trusted</warning>');
+                    if ($uid = getenv('SUDO_UID')) {
+                        // Silently clobber any sudo credentials on the invoking user to avoid privilege escalations later on
+                        // ref. https://github.com/composer/composer/issues/5119
+                        exec("sudo -u \\#{$uid} sudo -K > /dev/null 2>&1");
+                    }
+                }
+                // Silently clobber any remaining sudo leases on the current user as well to avoid privilege escalations
+                exec("sudo -K > /dev/null 2>&1");
+            }
+
             // switch working dir
             if ($newWorkDir = $this->getNewWorkingDir($input)) {
                 $oldWorkingDir = getcwd();