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Hi,
I think the issue Jeff is trying to highlight is similar to a posting
we made in November last year regarding session IDs and middleware
applications. Jeff has requested me to post the advisory to hopefully
give everyone a better understanding of what he was trying to
explain. Below is the original advisory that was posted on the 21st
November 2000. There are also some interesting replies to the posting
that can be found by looking through the archives.
- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
MIS Corporate Defence Solutions - NST Advisory (001)
Possible session hijacking with website implementations
using middleware products.
Written: 13/11/00
Revised: 20/11/00
Released: 21/11/00
- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Systems affected:
- -----------------
Any web systems / farms utilising middleware software to help run all
or
parts of their website using some form of session id tokens that are
stored
within the URL.
Affected:
- ---------
Users that visit websites that are affected (see above).
Vendor status:
- --------------
N/A - no single vendor.
However, BroadVision was contacted about this issue and they are
aware of
this problem. They are currently implementing changes and
recommendations to
it's customers as you read.
Overview:
- ---------
There are a number of companies that utilise middleware software
within
their websites / farms, due to the "all-in-one" nature of the
packages on
offer. Some of the features (not naming all of them) allow a company
to
track user's browsing and buying habits throughout their site,
tailored
content depending on the visitor, and real-time analytic reports.
This issue seems not to be publicised and from conversations we have
had
with people at the software houses, they seem to be sweeping this
under the
carpet and changing their systems on the quiet.
Issue:
- ------
BroadVision will be used as our example middleware product because it
is the
one we have been using for testing. An example site of www.site.com
utilising BroadVision software, passes it's parameters required for
identification into JavaScript Pages (.jsp) that display site content
and
run any back-end commands / applications that may be required. We
assume
from here on, that www.site.com is an e-commerce and a service
provider of
some sort.
When a user views a site using BroadVision as well as Session IDs and
Engine
IDs to display content, the IDs are present within the URL. From the
limited
experience we have had with BroadVision, it seems that the session ID
is a
random 20 digit number (xxxxxxxxxx.xxxxxxxxxx) and the Engine ID
represents
what server is serving the content. Therefore it can be determined
how many
servers are presenting the content. The first part (10 digits) of the
BV_SessionID is a random number. The second part (10 digits) however,
seems
to be an incremental counter that could be used as a primary key in a
database or as a reference:
An example where the engine IDs are constant (taken from a sample of
100
hits):
BV_SessionID BV_EngineID
2nd part
^^^^^^^^^^
0857833937.0974830784 caljgjejmdfbekfcflcfhfcggl.0
2030451565.0974830918 caljgjejmdfbekfcflcfhfcggl.0
0013750567.0974830947 caljgjejmdfbekfcflcfhfcggl.0
1966354090.0974830997 caljgjejmdfbekfcflcfhfcggl.0
An example where the engine IDs are different (sequential hits from a
sample
of 100 hits):
2nd part
^^^^^^^^^^
0303470036.0974831433 kaljgjejmfmbekfcflcfhfcggm.0
1662867632.0974831449 ialjgjejmfkbekfcflcfhfcggm.0
0534620068.0974831462 faljgjejmfhbekfcflcfhfcggm.0
0325859633.0974831480 haljgjejmfjbekfcflcfhfcggm.0
1626080627.0974831494 galjgjejmfibekfcflcfhfcggm.0
0654920185.0974831506 ealjgjejmehbekfcflcfhfcggm.0
1323165012.0974831517 laljgjejmgebekfcflcfhfcggm.0
For example, visit www.site.com that is running Broadvision software.
You
will notice that your address bar will read something like this:
http://www.site.com/cgi-bin/iminst2-1/dev/globalframe.jsp?browser=4&pl
ugin=no&startcat=/Main&startloc=%2fdev%2fsinglecontent.jsp%3fid%3dpage
_home%26type%3dEDITORIAL%26property%3dCONTENT_TXT%26fullimage%3dtrue%2
6crmb%3dcrumb_home&lit=cre&titl=THE+Site+-+price+lists&BV_SessionID=@@
@@0265483420.0974078984@@@@&BV_EngineID=haljfclmegjbekfcflcfhfcggm.0
(this will be wrapped :( ) The important part of this URL is:
...
&BV_SessionID=@@@@0265483420.0974078984@@@@&BV_EngineID=haljfclmegjbek
fcflcfhfcggm.0
For other middleware applications, the parameter name might be &IdKey
or
&SessionID.
It is possible to derive the number of engines or servers that serve
pages
for www.site.com. This is derived from the way the engine ids are
structured.
The problem exists when a user is viewing www.site.com in normal HTTP
mode
and decides to move into the secure area of the site (HTTPS), such as
logging in to check your bill / account details for the service been
provided by www.site.com. The session ID that the user has remains
the same,
so in essence, follows him/herself into the secure zone.
Therefore, if you were able to sniff the BV_SessionID and BV_EngineID
parameters whilst the user is still browsing the "unsecure" area of
the
site, it is possible to "hijack" or "join" the session by replacing
the ID
strings within any of the URLs displayed in the address bar,
providing the
session timeout hasn't expired. The "hijack" or "join" is possible
from
either the same IP address or from a different IP address.
By registering yourself as a valid customer of www.site.com, it is
possible
to determine the full URL for accessing say a user's billing details,
billing address, etc... This will enable a malicious user to insert a
stolen
set of ids into the URL to gain unauthorised access to another
customers
data.
Please note that retrieving a list of valid BV_EngineIDs is trivial.
Just
repeatedly close and open a browser and take a note of the value.
Both the
session and engine IDs would be trivial to pick up if you knew users
were
visiting www.site.com on a LAN for example. Set up a sniffer,
retrieve the
IDs and hey presto! Although this is not as widespread as a number of
other
website / middleware vulnerabilities, we still deem this as a large
security
issue that is largely undocumented.
In theory, it is possible to brute force the BV_SessionID if there
are no
restrictions on the server side, and the client side has enough
bandwidth
available. Although this would take some time to brute force a
randomly
generated 20 digit number, it may be possible for an evil cracker to
get
lucky. If you specify an invalid session id / engine id or your
session has
timed out, an error is displayed (applicable to this example, may
differ
from implementation to implementation).
Workaround / Fix / Solution:
- ----------------------------
There is no silver bullet solution, but a number of workarounds can
be
applied to prevent this type of session hijacking.
1) Send all HTTP communication containing the session and engine ids
over
HTTPS to help prevent them from being "stolen".
2) Utilise a session cookie, i.e. a cookie that is linked to the
middleware's session management system. The cookie will contain the
session
ID details. Each time a user visits the page, the middleware
application
should check for the existance of this cookie and verify the values
held
within the cookie against the ones held within it's own internal
system. If
they are the same, it is a valid request. However if they are not the
same
or the cookie does not exist, this is not a valid request and should
be
declined. Please note that with some middleware software, it may be
the
responsibility of the web application running on top of the
middleware
software, to utilise a library that enables session cookies to be
utilised.
Please check with the vendor regarding this.
3) Utilise URL re-writing to prevent the contents of the query string
from
appearing in the URL that is displayed in the address bar of a
browser.
4) When a user is directed into the secure area of www.site.com to
view
their account details, site.com should generate a new session id
within the
HTTPS request and reply. This prevents a user being followed into the
secure
area.
5) Request further documentation from the vendor on how to implement
a
higher level of security whilst using their middleware products. The
reasoning behind this is because BroadVision have further
documentation
available, but we understand clients need to request it.
Disclaimer:
- -----------
Nothing is 100% secure, the risk of being hacked / cracked is always
improbable, never impossible.
Thanks:
- -------
NST @ MIS.
Eric Golin, Kevin Wharton @ BroadVision
Steve Fagg.
Thanks for taking the time to read this advisory,
WWW:
- ----
http://www.mis-cds.com/news/corporate/20001121bv.html
Cheers,
Paul Rogers,
Network Security Analyst.
MIS Corporate Defence Solutions Limited
Tel: +44 (0)1622 723422 (Direct Line)
+44 (0)1622 723400 (Switchboard)
Fax: +44 (0)1622 728580
Website: http://www.mis-cds.com/
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