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Re: cookie draft available

From: Koen Holtman <koen@win.tue.nl>
Date: Sat, 20 Apr 1996 00:05:12 +0200 (MET DST)
Message-Id: <199604192205.AAA04634@wsooti04.win.tue.nl>
To: hardie@nasa.gov
Cc: dmk@allegra.att.com, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Ted Hardie:
>
>Dave,
>
[...]
>The list of Koen's dimensions for the
>solution space of stateful dialogs, for example, seems to be a useful
>thing for implementors to keep in mind, but I believe that the bullets
>would have to be fleshed out a good bit before someone who has not
>been following the discussion would be sure of what you meant.

Actually, I wrote this list as a checklist for seeing if a stateful
dialog _support_ mechanism (like cookies) is good enough.  So the list
is for the http-wg, not for implementers, and can be deleted from the
draft.  Fleshing it out is not worth the trouble I think.

[...] 
>In Section 8.2, you discuss Cookie spoofing, but I believe that you
>are missing at least one of the possible problems--the way domain
>matching is described, it appears that someone from the host sub.tld
>could successfully get or spoof cookies for anyhost.sub.tld .

Eek!   I believe you are right, we missed that case.  anyhost.sub.tld
would indeed get

      Cookie: $Version="1";
                      session_id="1234";
                      session_id="1111";
                                         ^^^^^No Domain=sub.tld here!

I believe NetScape's original cookie mechanism required a Domain= in
the Set-Cookie header in order for the session_id="1111" cookie set by
sub.tld to get sent to anyhost.sub.tld, but the current rules do not
require this.  

We could tweaks the draft to solve this: we could change the following
sentences from Section 4.3.4:

 The value for the      
 domain attribute must be the value from the Domain attribute, if any, of  
 the corresponding Set-Cookie response header.  Otherwise the attribute    
 should be omitted from the Cookie request header.  

into

 The value for the domain attribute must be the (default) value of the
 Domain attribute of the corresponding Set-Cookie response header, if
 this value is not equal to the request-host of the request to be
 sent.  Otherwise the attribute should be omitted from the Cookie
 request header.

But I think the above tweak would not be the best solution (and we do
need to solve this).  We could solve this, and better match current
use of domain=, and improve the readability of the draft in several
places, if we go for domain attributes which always start with a dot:

  Set-Cookie: session_id="1111";Domain=".sub.tld".

Only the default domain attribute, the request-host, would not start
with a dot.

I include editing instructions which would bring this about below.
Note that there also are two editing instructions which fix a mistake
and an oversight in the draft, these are unconnected to domains
starting with dots.

>                        Best Regards,
>                                Ted Hardie

Koen.

--snip--


#2.  TERMINOLOGY
#

Rewrite text below:

#Hosts can be specified either as an IP address or a FQHN string.
#Sometimes we compare one host with another.  Host A domain-matches host
#B if
#
#   * both hosts are IP addresses and their host strings match exactly;
#     or
#
#   * both hosts are FQHN strings and their host strings match exactly;
#     or
#
#   * both hosts are FQHN strings and host A's string has the form N.B,
#     where B is host B's FQHN string, and N is a name string that may     |
#     have embedded dots, but not leading or trailing dots.  If host B     |
#     has a leading dot, the leading dot is ignored.  (So, x.y.com         |
#     domain-matches .y.com.)
#
#Note that domain-match is not a commutative operation: a.b.c.com
#domain-matches c.com, but not the reverse.                                |

to:

Hosts can be specified either as an IP address or a FQHN string.
Sometimes we compare one host with a domain string.  Host A
domain-matches a domain B if

   * the host is an IP address and equals the domain string
     exactly;

   * the host is an FQHN string and equals the domain string
     exactly;

   * the host is an FQHN string which has the from NB, where 
     where B is the domain string, and N is non-empty string.
     (So the host x.y.com domain-matches the domain .y.com.).



#4.2.2  Set-Cookie Syntax  The syntax for the Set-Cookie response header

Rewrite

#Domain=domain
#     Optional.  The Domain attribute specifies the host and domain name
#     for which the cookie is valid.

to

Domain=domain
      Optional.  The Domain attribute specifies the domain for which
      the cookie is valid.  The domain must always start with a dot.


#4.3.2  Rejecting Cookies 
#
#To prevent possible security or privacy
#violations, a user agent rejects a cookie (shall not store its
#information) if any of the following is true:
#
#   * The value for the Path attribute is not a prefix of the request-
#     URI.

Insert here:

    *  A value for the Domain attribute was supplied in the
       Set-Cookie header, and this value does not start with a dot

#
#   * The value for the Domain attribute contains no embedded dots.        |
#
#   * The value for the request-host does not domain-match the Domain      *
#     attribute.
#

Rewrite text below:

#   * The request-host is a name (not IP address), D is the value of the
#     Domain attribute, and request-host has the form H.D, where H is a
#     string, and H contains one or more dots.                             |

to:

   * The request-host is a name (not IP address), D is the value of
     the Domain attribute, and request-host has the form HD,
     where H is a string, and H contains one or more dots.

#
#Examples:                                                                 |
#
#   * A Set-Cookie from request-host y.x.foo.com for Domain=foo.com would
#     be rejected, because H is y.x and contains a dot.                    |

Change Domain=foo.com above to Domain=.foo.com

#
#   * A Set-Cookie from request-host x.foo.com for Domain=foo.com would    |
#     be accepted.                                                         |

Change Domain=foo.com above to Domain=.foo.com

#
#   * A Set-Cookie with Domain=.com, Domain=com., or Domain=.com., will    |
#     always be rejected, because there is no embedded dot.

Delete `Domain=com., ' above.


#4.3.4  Sending Cookies to the Origin Server  

#Domain Selection
#     The Domain attribute of the cookie must domain-match the origin
#     server's fully-qualified host name.                                  *

OOPS!! The above text contains a mistake, it should be rewritten to:

 Domain Selection 
     The origin server's fully-qualified host name must
     domain-match the Domain attribute of the cookie.

even if we don't switch to domains starting with a dot.


#8.2  Cookie Spoofing
#
#Proper application design can avoid spoofing attacks from related         |
#domains.  Consider:
#
#  1.  User agent makes request to victim.hacker.edu, gets back cookie     |
#      session_id="1234" and sets the default domain victim.hacker.edu.

Oops!  Why did I not notice this sooner?  `hacker.edu' should of
course be `cracker.edu', or else old-time hackers will accuse us of
polluting their language.

Please do a global query-replace from `hacker.edu' to `cracker.edu'.

#  2.  User agent makes request to spoof.hacker.edu, gets back cookie      |
#      session-id="1111", with Domain="hacker.edu".                        |

Change Domain="hacker.edu" above to Domain=".cracker.edu"

#  3.  User agent makes request to victim.hacker.edu again, and passes     |
#
#      Cookie: $Version="1";                                               |
#                      session_id="1234";                                  |
#                      session_id="1111"; $Domain="hacker.edu"             |

Change Domain="hacker.edu" above to Domain=".cracker.edu"

#
#      The server at victim.hacker.edu should detect that the second       |
#      cookie was not one it originated by noticing that the Domain        |
#      attribute is not for itself and ignore it.
#
#8.3  Unexpected Cookie Sharing
#

Change the text:

#A user agent should make every attempt to prevent the sharing of session  |
#information between hosts that do not domain-match.

to:

A user agent should make every attempt to prevent the sharing of session  |
information between hosts that are not in the same domain.

That is all.
Received on Friday, 19 April 1996 15:12:01 EDT

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