diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 21ce72fd79c..ecb4e5a8f70 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -18,7 +18,7 @@ pardir = '..'
 extsep = '.'
 sep = '/'
 pathsep = ':'
-defpath = ':/bin:/usr/bin'
+defpath = '/bin:/usr/bin'
 altsep = None
 devnull = '/dev/null'
 
diff --git a/Misc/NEWS.d/next/Security/2019-01-17-10-03-48.bpo-35755.GmllIs.rst b/Misc/NEWS.d/next/Security/2019-01-17-10-03-48.bpo-35755.GmllIs.rst
new file mode 100644
index 00000000000..959aafd7344
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2019-01-17-10-03-48.bpo-35755.GmllIs.rst
@@ -0,0 +1,5 @@
+:func:`shutil.which` now uses ``os.confstr("CS_PATH")`` if available and if the
+:envvar:`PATH` environment variable is not set. Remove also the current
+directory from :data:`posixpath.defpath`. On Unix, :func:`shutil.which` and the
+:mod:`subprocess` module no longer search the executable in the current
+directory if the :envvar:`PATH` environment variable is not set.