CVE-2017-14604 (C, published 2017-09-20T08:29Z)
Description: value: GNOME Nautilus before 3.23.90 allows attackers to spoof a file type by using the .desktop file extension, as demonstrated by an attack in which a .desktop file's Name field ends in .pdf but this file's Exec field launches a malicious "sh -c" command. In other words, Nautilus provides no UI indication that a file actually has the potentially unsafe .desktop extension; instead, the UI only shows the .pdf extension. One (slightly) mitigating factor is that an attack requires the .desktop file to have execute permission. The solution is to ask the user to confirm that the file is supposed to be treated as a .desktop file, and then remember the user's answer in the metadata::trusted field.
Severity: MEDIUM (CVSS v3 base score: 6.5)
Weakness: CWE-20 \u2014 Improper Input Validation
The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
Repository: https://github.com/GNOME/nautilus
Files changed:
src/nautilus-directory-async.c
src/nautilus-file-operations.c
src/nautilus-file-operations.h
src/nautilus-metadata.c
src/nautilus-metadata.h
src/nautilus-mime-actions.c
Commit message: mime-actions: use file metadata for trusting desktop files

Currently we only trust desktop files that have the executable bit
set, and don't replace the displayed icon or the displayed name until
it's trusted, which prevents for running random programs by a malicious
desktop file.

However, the executable permission is preserved if the desktop file
comes from a compressed file.

To prevent this, add a metadata::trusted metadata to the file once the
user acknowledges the file as trusted. This adds metadata to the file,
which cannot be added unless it has access to the computer.

Also remove the SHEBANG "trusted" content we were putting inside the
desktop file, since that doesn't add more security since it can come
with the file itself.

https://bugzilla.gnome.org/show_bug.cgi?id=777991


Vulnerable code:
    if (nautilus_file_can_execute (file))
mark_desktop_file_trusted (CommonJob    *common,
                           GCancellable *cancellable,
                           GFile        *file,
                           gboolean      interactive);
            mark_desktop_file_trusted (job,
                                       job->cancellable,
                                       dest,
                                       FALSE);
mark_trusted_task_done (GObject      *source_object,
                        GAsyncResult *res,
                        gpointer      user_data)
mark_desktop_file_trusted (CommonJob    *common,
                           GCancellable *cancellable,
                           GFile        *file,
                           gboolean      interactive)
    char *contents, *new_contents;
    gsize length, new_length;
    error = NULL;
    if (!g_file_load_contents (file,
                               cancellable,
                               &contents, &length,
                               NULL, &error))
    {
        if (interactive)
        {
            response = run_error (common,
                                  g_strdup (_("Unable to mark launcher trusted (executable)")),
                                  error->message,
                                  NULL,
                                  FALSE,
                                  CANCEL, RETRY,
                                  NULL);
        }
        else
        {
            response = 0;
        }


        if (response == 0 || response == GTK_RESPONSE_DELETE_EVENT)
        {
            abort_job (common);
        }
        else if (response == 1)
        {
            goto retry;
        }
        else
        {
            g_assert_not_reached ();
        }

        goto out;
    }

    if (!g_str_has_prefix (contents, "#!"))
    {
        new_length = length + strlen (TRUSTED_SHEBANG);
        new_contents = g_malloc (new_length);

        strcpy (new_contents, TRUSTED_SHEBANG);
        memcpy (new_contents + strlen (TRUSTED_SHEBANG),
                contents, length);

        if (!g_file_replace_contents (file,
                                      new_contents,
                                      new_length,
                                      NULL,
                                      FALSE, 0,
                                      NULL, cancellable, &error))
        {
            g_free (contents);
            g_free (new_contents);

            if (interactive)
            {
                response = run_error (common,
                                      g_strdup (_("Unable to mark launcher trusted (executable)")),
                                      error->message,
                                      NULL,
                                      FALSE,
                                      CANCEL, RETRY,
                                      NULL);
            }
            else
            {
                response = 0;
            }

            if (response == 0 || response == GTK_RESPONSE_DELETE_EVENT)
            {
                abort_job (common);
            }
            else if (response == 1)
            {
                goto retry;
            }
            else
            {
                g_assert_not_reached ();
            }

            goto out;
        }
        g_free (new_contents);
    }
    g_free (contents);
mark_trusted_task_thread_func (GTask        *task,
                               gpointer      source_object,
                               gpointer      task_data,
                               GCancellable *cancellable)
    mark_desktop_file_trusted (common,
                               cancellable,
                               job->file,
                               job->interactive);
nautilus_file_mark_desktop_file_trusted (GFile              *file,
                                         GtkWindow          *parent_window,
                                         gboolean            interactive,
                                         NautilusOpCallback  done_callback,
                                         gpointer            done_callback_data)
    task = g_task_new (NULL, NULL, mark_trusted_task_done, job);
    g_task_run_in_thread (task, mark_trusted_task_thread_func);
void nautilus_file_mark_desktop_file_trusted (GFile           *file,
					      GtkWindow        *parent_window,
					      gboolean          interactive,
					      NautilusOpCallback done_callback,
					      gpointer          done_callback_data);
#define RESPONSE_MARK_TRUSTED 1003
        case RESPONSE_RUN:
        }
        break;

        case RESPONSE_MARK_TRUSTED:
        {
            file = nautilus_file_get_location (parameters->file);
            nautilus_file_mark_desktop_file_trusted (file,
                                                     parameters->parent_window,
                                                     TRUE,
                                                     NULL, NULL);
                               _("_Launch Anyway"), RESPONSE_RUN);
                                   _("Mark as _Trusted"), RESPONSE_MARK_TRUSTED);
        gtk_dialog_add_button (GTK_DIALOG (dialog),
                               _("_Cancel"), GTK_RESPONSE_CANCEL);
        gtk_dialog_set_default_response (GTK_DIALOG (dialog), GTK_RESPONSE_CANCEL);


Fixed code:
#include "nautilus-metadata.h"
    g_autofree gchar* trusted = NULL;
    trusted = nautilus_file_get_metadata (file,
                                          NAUTILUS_METADATA_KEY_DESKTOP_FILE_TRUSTED,
                                          NULL);
    if (nautilus_file_can_execute (file) && trusted != NULL)
mark_desktop_file_executable (CommonJob    *common,
                              GCancellable *cancellable,
                              GFile        *file,
                              gboolean      interactive);
            mark_desktop_file_executable (job,
                                          job->cancellable,
                                          dest,
                                          FALSE);
mark_desktop_file_executable_task_done (GObject      *source_object,
                                        GAsyncResult *res,
                                        gpointer      user_data)
mark_desktop_file_executable (CommonJob    *common,
                              GCancellable *cancellable,
                              GFile        *file,
                              gboolean      interactive)
    error = NULL;
mark_desktop_file_executable_task_thread_func (GTask        *task,
                                               gpointer      source_object,
                                               gpointer      task_data,
                                               GCancellable *cancellable)
    mark_desktop_file_executable (common,
                                  cancellable,
                                  job->file,
                                  job->interactive);
nautilus_file_mark_desktop_file_executable (GFile              *file,
                                            GtkWindow          *parent_window,
                                            gboolean            interactive,
                                            NautilusOpCallback  done_callback,
                                            gpointer            done_callback_data)
    task = g_task_new (NULL, NULL, mark_desktop_file_executable_task_done, job);
    g_task_run_in_thread (task, mark_desktop_file_executable_task_thread_func);
void nautilus_file_mark_desktop_file_executable (GFile           *file,
                                                 GtkWindow        *parent_window,
                                                 gboolean          interactive,
                                                 NautilusOpCallback done_callback,
                                                 gpointer          done_callback_data);
    NAUTILUS_METADATA_KEY_DESKTOP_FILE_TRUSTED,
#define NAUTILUS_METADATA_KEY_DESKTOP_FILE_TRUSTED				"trusted"

#include "nautilus-metadata.h"
        case GTK_RESPONSE_OK:
            file = nautilus_file_get_location (parameters->file);

            /* We need to do this in order to prevent malicious desktop files
             * with the executable bit already set.
             * See https://bugzilla.gnome.org/show_bug.cgi?id=777991
             */
            nautilus_file_set_metadata (parameters->file, NAUTILUS_METADATA_KEY_DESKTOP_FILE_TRUSTED,
                                        NULL,
                                        "yes");

            nautilus_file_mark_desktop_file_executable (file,
                                                        parameters->parent_window,
                                                        TRUE,
                                                        NULL, NULL);

            /* Need to force a reload of the attributes so is_trusted is marked
             * correctly. Not sure why the general monitor doesn't fire in this
             * case when setting the metadata
             */
            nautilus_file_invalidate_all_attributes (parameters->file);


                               _("_Cancel"), GTK_RESPONSE_CANCEL);

        gtk_dialog_set_default_response (GTK_DIALOG (dialog), GTK_RESPONSE_CANCEL);
                                   _("Trust and _Launch"), GTK_RESPONSE_OK);