From https://ftp.gnu.org/gnu/bash/bash-4.4-patches/bash44-006

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

			     BASH PATCH REPORT
			     =================

Bash-Release:	4.4
Patch-ID:	bash44-006

Bug-Reported-by:	<fernando@null-life.com>
Bug-Reference-ID:	<CAEr-gPFPvqheiAeENmMkEwWRd4U=1iqCsYmR3sLdULOqL++_tQ@mail.gmail.com>
Bug-Reference-URL:	

Bug-Description:

Out-of-range negative offsets to popd can cause the shell to crash attempting
to free an invalid memory block.

Patch (apply with `patch -p0'):

*** bash-4.4-patched/builtins/pushd.def	2016-01-25 13:31:49.000000000 -0500
--- b/builtins/pushd.def	2016-10-28 10:46:49.000000000 -0400
***************
*** 366,370 ****
      }
  
!   if (which > directory_list_offset || (directory_list_offset == 0 && which == 0))
      {
        pushd_error (directory_list_offset, which_word ? which_word : "");
--- b/366,370 ----
      }
  
!   if (which > directory_list_offset || (which < -directory_list_offset) || (directory_list_offset == 0 && which == 0))
      {
        pushd_error (directory_list_offset, which_word ? which_word : "");
***************
*** 388,391 ****
--- b/388,396 ----
  	 of the list into place. */
        i = (direction == '+') ? directory_list_offset - which : which;
+       if (i < 0 || i > directory_list_offset)
+ 	{
+ 	  pushd_error (directory_list_offset, which_word ? which_word : "");
+ 	  return (EXECUTION_FAILURE);
+ 	}
        free (pushd_directory_list[i]);
        directory_list_offset--;
*** bash-4.4/patchlevel.h	2016-06-22 14:51:03.000000000 -0400
--- b/patchlevel.h	2016-10-01 11:01:28.000000000 -0400
***************
*** 26,30 ****
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 5
  
  #endif /* _PATCHLEVEL_H_ */
--- b/26,30 ----
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 6
  
  #endif /* _PATCHLEVEL_H_ */