diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -1383,6 +1383,11 @@ class gitsubrepo(abstractsubrepo):
         are not supported and very probably fail.
         """
         self.ui.debug('%s: git %s\n' % (self._relpath, ' '.join(commands)))
+        if env is None:
+            env = os.environ.copy()
+        # fix for Git CVE-2015-7545
+        if 'GIT_ALLOW_PROTOCOL' not in env:
+            env['GIT_ALLOW_PROTOCOL'] = 'file:git:http:https:ssh'
         # unless ui.quiet is set, print git's stderr,
         # which is mostly progress and useful info
         errpipe = None
diff --git a/tests/test-subrepo-git.t b/tests/test-subrepo-git.t
--- a/tests/test-subrepo-git.t
+++ b/tests/test-subrepo-git.t
@@ -1132,4 +1132,36 @@ make sure we show changed files, rather 
   ? s/foobar.orig
   ? s/snake.python.orig
 
+test for Git CVE-2016-3068
+  $ hg init malicious-subrepository
+  $ cd malicious-subrepository
+  $ echo "s = [git]ext::sh -c echo% pwned% >&2" > .hgsub
+  $ git init s
+  Initialized empty Git repository in $TESTTMP/tc/malicious-subrepository/s/.git/
+  $ cd s
+  $ git commit --allow-empty -m 'empty'
+  [master (root-commit) 153f934] empty
   $ cd ..
+  $ hg add .hgsub
+  $ hg commit -m "add subrepo"
+  $ cd ..
+  $ env -u GIT_ALLOW_PROTOCOL hg clone malicious-subrepository malicious-subrepository-protected
+  Cloning into '$TESTTMP/tc/malicious-subrepository-protected/s'...
+  fatal: transport 'ext' not allowed
+  updating to branch default
+  cloning subrepo s from ext::sh -c echo% pwned% >&2
+  abort: git clone error 128 in s (in subrepo s)
+  [255]
+
+whitelisting of ext should be respected (that's the git submodule behaviour)
+  $ env GIT_ALLOW_PROTOCOL=ext hg clone malicious-subrepository malicious-subrepository-clone-allowed
+  Cloning into '$TESTTMP/tc/malicious-subrepository-clone-allowed/s'...
+  pwned
+  fatal: Could not read from remote repository.
+  
+  Please make sure you have the correct access rights
+  and the repository exists.
+  updating to branch default
+  cloning subrepo s from ext::sh -c echo% pwned% >&2
+  abort: git clone error 128 in s (in subrepo s)
+  [255]