diff -r 173ecccb9ee7 -r ca398a50ca00 mercurial/subrepo.py
--- a/mercurial/subrepo.py	Mon Jul 31 16:44:17 2017 -0700
+++ b/mercurial/subrepo.py	Mon Jul 31 14:55:11 2017 -0700
@@ -1543,6 +1543,9 @@
 
     def _fetch(self, source, revision):
         if self._gitmissing():
+            # SEC: check for safe ssh url
+            util.checksafessh(source)
+
             source = self._abssource(source)
             self.ui.status(_('cloning subrepo %s from %s\n') %
                             (self._relpath, source))