Mercurial > thoughts

     1 #+title: Password Security in Emacs Terminal Emulators

     2 #+author: Robert McIntyre

     3 #+email: rlm@mit.edu

     4 #+description: emacs terminal password security

     5 #+keywords: emacs, password, security, term

     6 #+SETUPFILE: ../../aurellem/org/setup.org

     7 #+INCLUDE: ../../aurellem/org/level-0.org

     8 #+babel: :mkdirp yes :noweb yes :exports both

     9 

    10 I use emacs for everything -- email, programming, document

    11 preparation, planning... You name it, I do it! One thing which I use

    12 emacs for is terminal emulation, which is where you create a buffer in

    13 emacs where you can enter commands as if the buffer were a

    14 terminal. Good terminal emulation packages for emacs include

    15 =multi-term= and =term=.

    16 

    17 * Watch Out for =view-lossage=!

    18 However, if you are going to use terminal emulation in emacs, you have

    19 to be careful around "sudo" prompts, and when logging into other

    20 servers using ssh, because /the last 300 keystrokes you have typed in

    21 emacs are available/ using =C-h l=, a help function in emacs which

    22 displays the last keypresses you have typed.

    23 

    24 #+begin_example

    25 C-h l runs the command view-lossage, which is an interactive compiled

    26 Lisp function in `help.el'.

    27 

    28 It is bound to C-h l, <help> l.

    29 

    30 (view-lossage)

    31 

    32 Display last 300 input keystrokes.

    33 #+end_example

    34 

    35 Let's say my password is "sup3r-seekrit#7".

    36 

    37 I open an emacs terminal using =M-x multi-term=, then do the following

    38 

    39 #+begin_example

    40 [~] $ ssh rlm@linerva.mit.edu

    41 Password: 

    42 

    43 Welcome to Linerva, the SIPB Linux dialup for MIT.

    44 Linerva runs Debathena on Debian squeeze.

    45  http://linerva.mit.edu                           for more information

    46  blanche linerva-announce -a $USER          # for outage announcements

    47  linerva@mit.edu              (not IS&T) for questions and bug reports

    48 

    49 Last login: Mon Mar  4 12:53:23 2013 from ella.csail.mit.edu

    50 rlm@dr-wily:~$ exit

    51 logout

    52 Connection to linerva.mit.edu closed.

    53 #+end_example

    54 

    55 Now, when I type =C-h l=, I can see this:

    56 

    57 #+begin_example

    58 s s h SPC r l m @ l i n e r v a . m i t . e d u <return>

    59 s u p 3 r - s e e k r i t # 7 <return> e x i t C-h l

    60 #+end_example

    61 

    62 Needless to say, this can be a security vulnerability.

    63 

    64 * Solutions to this problem

    65 

    66  - If you don't ever type your password into an emacs terminal buffer,

    67    then you are not at risk. This can be accomplished by using ssh

    68    keyfiles or Kerberos for connecting to remote servers, and by

    69    enabling passwordless sudo.

    70 

    71  - You can disable emacs keylogging, though you then won't be able to

    72    use the =view-lossage= command anymore.

    73 

    74  - If there's no way for an attacker to get into your emacs process,

    75    then your passwords are safe. Still, you run the risk of someone

    76    physically near your computer using this method to view your

    77    password, as well as inadvertently exposing your password when

    78    showing someone what =view-lossage= does!

    79 

    80 * Source Listing

    81 #+html: <ul> <li> <a href="../org/emacs-password.org">This org file</a> </li> </ul>

    82 

    83     

    84 

    85 

    86
author	Robert McIntyre <rlm@mit.edu>
date	Thu, 05 Feb 2015 23:05:45 -0800
parents	8a5b6ca53764
children