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1 #+title: Password Security in Emacs Terminal Emulators
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2 #+author: Robert McIntyre
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3 #+email: rlm@mit.edu
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4 #+description: emacs terminal password security
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5 #+keywords: emacs, password, security, term
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6 #+SETUPFILE: ../../aurellem/org/setup.org
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7 #+INCLUDE: ../../aurellem/org/level-0.org
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8 #+babel: :mkdirp yes :noweb yes :exports both
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9
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10 I use emacs for everything -- email, programming, document
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11 preparation, planning... You name it, I do it! One thing which I use
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12 emacs for is terminal emulation, which is where you create a buffer in
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13 emacs where you can enter commands as if the buffer were a
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14 terminal. Good terminal emulation packages for emacs include
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15 =multi-term= and =term=.
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16
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17 * Watch Out for =view-lossage=!
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18 However, if you are going to use terminal emulation in emacs, you have
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19 to be careful around "sudo" prompts, and when logging into other
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20 servers using ssh, because /the last 300 keystrokes you have typed in
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21 emacs are available/ using =C-h l=, a help function in emacs which
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22 displays the last keypresses you have typed.
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23
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24 #+begin_example
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25 C-h l runs the command view-lossage, which is an interactive compiled
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26 Lisp function in `help.el'.
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27
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28 It is bound to C-h l, <help> l.
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29
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30 (view-lossage)
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31
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32 Display last 300 input keystrokes.
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33 #+end_example
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34
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35 Let's say my password is "sup3r-seekrit#7".
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36
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37 I open an emacs terminal using =M-x multi-term=, then do the following
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38
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39 #+begin_example
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40 [~] $ ssh rlm@linerva.mit.edu
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41 Password:
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42
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43 Welcome to Linerva, the SIPB Linux dialup for MIT.
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44 Linerva runs Debathena on Debian squeeze.
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45 http://linerva.mit.edu for more information
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46 blanche linerva-announce -a $USER # for outage announcements
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47 linerva@mit.edu (not IS&T) for questions and bug reports
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48
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49 Last login: Mon Mar 4 12:53:23 2013 from ella.csail.mit.edu
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50 rlm@dr-wily:~$ exit
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51 logout
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52 Connection to linerva.mit.edu closed.
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53 #+end_example
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54
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55 Now, when I type =C-h l=, I can see this:
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56
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57 #+begin_example
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58 s s h SPC r l m @ l i n e r v a . m i t . e d u <return>
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59 s u p 3 r - s e e k r i t # 7 <return> e x i t C-h l
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60 #+end_example
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61
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62 Needless to say, this can be a security vulnerability.
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63
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64 * Solutions to this problem
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65
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66 - If you don't ever type your password into an emacs terminal buffer,
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67 then you are not at risk. This can be accomplished by using ssh
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68 keyfiles or Kerberos for connecting to remote servers, and by
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69 enabling passwordless sudo.
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70
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71 - You can disable emacs keylogging, though you then won't be able to
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72 use the =view-lossage= command anymore.
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73
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74 - If there's no way for an attacker to get into your emacs process,
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75 then your passwords are safe. Still, you run the risk of someone
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76 physically near your computer using this method to view your
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77 password, as well as inadvertently exposing your password when
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78 showing someone what =view-lossage= does!
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79
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80 * Source Listing
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81 #+html: <ul> <li> <a href="../org/emacs-password.org">This org file</a> </li> </ul>
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82
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84
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