Change ASPSessionID

[Joseph Shoe]

How do you change the ASPSessionID during a web session? I have an ASP
application in SSL. The first screen is a login screen, which requests user
id and password. An ASPSessionID is assigned for this page. Once the user
is authenticated by valid id/pwd, the second page starts the real
applicaiton. I want to change the ASPSessionID to be different from the
first login page, which was issued to an unauthenticated user. How do I do
that in ASP?

Thanks.
Joseph

[Aaron Bertrand [SQL Server MVP]]

> Thanks, Tim. Your description is mostly correct. One clarificaiton: when

PC2 is able to get to the protected page of PC1 using the same SessionID,
the
session variable "logged in" would be yes for PC2, as seen by PC1.

I am not sure I understand how you expect a user on PC2 to be able to
install some javascript bookmarklet thing on PC1 or on your server in order
to find out his sessionID. If the user of PC2 has access to PC1, couldn't
he just use that access to find out the user's password (which he probably
has in a file somewhere, or on a sticky note on his monitor) or just take
over his session from there? There is nothing you can do in ASP to make a
user's workstation more secure. Of course it's easy to emulate this when
you're in control of both PC1 and PC2, as well as the web server. I don't
think it's even remotely likely in the real world. But I can't tell you
what to focus your energy on.

[Roland Hall]

"Tim Williams" wrote in message
news:u%******** ********@TK2MSF TNGP09.phx.gbl. ..
: alert (document.cooki e);
:
: works if I remember correctly. The cookie can be set in similar
: fashion (eg) using a js bookmarklet. Since you would then have the
: "correct" SessionId why couldn't you access the other session?

You remember correctly but it gives you access to YOUR session ID, not
someone else's Is it possible that you could be compromised and an attacker
could get this info? Sure, it's possible but if that is the case, they
don't need your session ID, they'll just install a keylogger and call it a
day.

Could a man in the middle attack exploit this? Sure but critical
information is generally transmitted encrypted using SSL so the man in the
middle doesn't get anything. Even if you had an encrypted connection, if
your system is compromised it doesn't matter what you security measures are
between you and the web site. At that point the game's over.

--
Roland Hall
/* This information is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of merchantability
or fitness for a particular purpose. */
Technet Script Center - http://www.microsoft.com/technet/scriptcenter/
WSH 5.6 Documentation - http://msdn.microsoft.com/downloads/list/webdev.asp
MSDN Library - http://msdn.microsoft.com/library/default.asp

[tom_shoelace]

Aaron Bertrand [SQL Server MVP] wrote:

Thanks, Tim. Your description is mostly correct. One clarificaiton: when
PC2 is able to get to the protected page of PC1 using the same SessionID,
the
session variable "logged in" would be yes for PC2, as seen by PC1.
I am not sure I understand how you expect a user on PC2 to be able to
install some javascript bookmarklet thing on PC1 or on your server in order
to find out his sessionID. If the user of PC2 has access to PC1, couldn't
he just use that access to find out the user's password (which he probably
has in a file somewhere, or on a sticky note on his monitor) or just take
over his session from there? There is nothing you can do in ASP to make a
user's workstation more secure. Of course it's easy to emulate this when
you're in control of both PC1 and PC2, as well as the web server. I don't
think it's even remotely likely in the real world. But I can't tell you
what to focus your energy on.

I agree with Aaron.

If a third party can get the ASPSessionid, then they can get a second
one later, or a third, and so on. Also if a third party can get the
ASPSessionid, then they can also get a cookie or any other saved item
on the client. All data passes through the browser and is visible
there.

Your question can be paraphrased as
"How do I transfer data to the user without
passing it through a client browser where
my mysterious secrets will be compromised."

This makes no sense: you're chasing your own ignorance but it has
outsmarted you. You are like the man who tries to catch a fart in a
butterfly net.

[Tim Williams]

I'm "mostly correct" ? I think just "correct" would do fine. PC2
does not "get to the protected page of PC1" - it can access any
protected page *on the server*, but has no access to PC1 at all.

Maybe my original summary was unclear....

Tim.
"Joseph Shoe" <Jo********@dis cussions.micros oft.com> wrote in message
news:C0******** *************** ***********@mic rosoft.com...

Thanks, Tim. Your description is mostly correct. One
clarificaiton: when
PC2 is able to get to the protected page of PC1 using the same
SessionID, the
session variable "logged in" would be yes for PC2, as seen by PC1.
PC2 will
not be redirected to the login page.

Your suggestion of using a second session cookie is a sound one. I
was
merely looking for a shortcut. Afterall, it shouldn't be much
difficult for
ASP to provide an API to change the SessionID.

"Tim Williams" wrote:

So said so done. Exactly as described.

Opened login page on PC1, copied sessionid cookie name/value to
text
file. Then logged in on PC1 using a known UN/PW.

Few minutes later on PC2, used an "edit cookie" bookmarklet to
create
the session cookie from PC1, and was able to bypass the login page
and
go directly to a "protected" page. This page would normally (on
seeing there is no "logged in=yes" session variable) redirect me to
the login page but in this case the session from PC1 is referenced
due
to the copied cookie.

Bookmarklet for editing the session cookie was from here:
http://visitjesper.homeip.net/bookmarklets.html

However unlikely the scenario, it has to be admitted to be possible
(and not that difficult either). That is the only point I'm trying
to
make here.
Easy to prevent just by adding another session cookie on login and
checking for both that *and* the session variable, rather than
relying
only on the session variable.

Tim.
"Aaron Bertrand [SQL Server MVP]" <te*****@dnartr eb.noraa> wrote in
message news:uU******** ******@TK2MSFTN GP14.phx.gbl...

>> works if I remember correctly. The cookie can be set in
>> similar
>> fashion (eg) using a js bookmarklet. Since you would then have
>> the
>> "correct" SessionId
>
> Well, let me know exactly how you plan to do it. See if you can
> set
> a session variable for a browser on one machine, get the cookie
> without having access to the ASP file(s) directly, then use
> another
> machine and fiddle with the cookie however you see fit, and see
> if
> you can retrieve the session variable on machine B that was set
> for
> the user on machine A.
>
> My experiments in the past have proved to me that it will not
> work.
>
> In any case, even if the above were to work, a malicious user
> would
> have to have access to the first user's session to get their
> sessionID at all, and if they can do that, why not just continue
> their session?
>

[Roland Hall]

<to**********@y ahoo.com> wrote in message
news:11******** **************@ g47g2000cwa.goo glegroups.com.. .
This makes no sense: you're chasing your own ignorance but it has
: outsmarted you. You are like the man who tries to catch a fart in a
: butterfly net.

(O:=

--
Roland Hall
/* This information is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of merchantability
or fitness for a particular purpose. */
Technet Script Center - http://www.microsoft.com/technet/scriptcenter/
WSH 5.6 Documentation - http://msdn.microsoft.com/downloads/list/webdev.asp
MSDN Library - http://msdn.microsoft.com/library/default.asp

[Roland Hall]

"Tim Williams" wrote in message
news:eG******** ******@TK2MSFTN GP09.phx.gbl...
: I'm "mostly correct" ? I think just "correct" would do fine. PC2
: does not "get to the protected page of PC1" - it can access any
: protected page *on the server*, but has no access to PC1 at all.
:
: Maybe my original summary was unclear....

Nah, everything you've said is. This is where the term script kiddie comes
from.

--
Roland Hall
/* This information is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of merchantability
or fitness for a particular purpose. */
Technet Script Center - http://www.microsoft.com/technet/scriptcenter/
WSH 5.6 Documentation - http://msdn.microsoft.com/downloads/list/webdev.asp
MSDN Library - http://msdn.microsoft.com/library/default.asp

[Michael D. Kersey]

Tim Williams wrote:

<snipped>

Easy to prevent just by adding another session cookie on login and
checking for both that *and* the session variable, rather than relying
only on the session variable.
Tim.

But it can't be just _any_ cookie! We must test the _contents_ of the
cookie and not merely its presence.

The cookie's contents should not be predictable by the attacker. Storing
the username or SSN in a cookie would be ineffective because an attacker
(who already has my ASPSessionID) might then easily mimic my cookie too.

And the serverside code must check the cookie's contents on each page.
So the cookie value must also be stored somewhere on the server (Session
variable, database, file, or Application variable(s), etc.).

So it seems a relatively easy method to thwart the "session fixation
attack" would be, immediately after the user is authenticated, to
- set a cookie to some random value XXXXX,
- set a Session variable to the same value XXXXX,
[From a security standpoint, the cookie is a "client key" and the
Session variable is a "server key"]. Then, on every page, check that the
cookie and Session variable match.

Kudos
- to Joseph Shoe (Joe Hsu) for bringing this problem to the table and
- to Tim for presenting tools and ways to manifest the problem
and to both of you for showing how to solve the problem:
I found no mention of session fixation attacks on the Microsoft
newsgroups prior to Joseph's. Nor could a quick search find anything on
Microsoft's site.

Here's a discussion, with diagrams, of the "session fixation attack":
http://shiflett.org/articles/security-corner-feb2004

I am curious whether ASP.NET is vulnerable to this attack.

Google search shows that knowledge about such attacks has been present
since at least 2001. http://www.tisc2001.com/newsletters/53.html
shows how a session fixation attack is set up [hint: the scenario we've
been discussing isn't the important one]. I don't believe that this
older paper explicitly considers the case of a legitimate user who
wishes to mimic another legitimate user and thereby gain illegitimate
access. And here's an update and PDF paper by the same authors:
http://www.acrossecurity.com/papers.htm

Here's another article:
http://archives.neohapsis.com/archiv...2-q4/0117.html

IMO this "session fixation attack" is both interesting and a serious
problem for ASP applications. It seems especially pertinent to intranets
where secure information is maintained internally and where security
must not be breached. That is the most common scenario for stealing
information.

We need to talk about this more.

[Tim Williams]

Michael,

Thanks for the links. This was not something I was aware of until
this thread, so it's been a useful exercise all round.

Off to read your references....

Cheers,
Tim
"Michael D. Kersey" <md******@hal-pc.org> wrote in message
news:uT******** ******@tk2msftn gp13.phx.gbl...

Tim Williams wrote:

<snipped>

Easy to prevent just by adding another session cookie on login and
checking for both that *and* the session variable, rather than
relying only on the session variable.
Tim.

But it can't be just _any_ cookie! We must test the _contents_ of
the cookie and not merely its presence.

The cookie's contents should not be predictable by the attacker.
Storing the username or SSN in a cookie would be ineffective because
an attacker (who already has my ASPSessionID) might then easily
mimic my cookie too.

And the serverside code must check the cookie's contents on each
page. So the cookie value must also be stored somewhere on the
server (Session variable, database, file, or Application
variable(s), etc.).

So it seems a relatively easy method to thwart the "session fixation
attack" would be, immediately after the user is authenticated, to
- set a cookie to some random value XXXXX,
- set a Session variable to the same value XXXXX,
[From a security standpoint, the cookie is a "client key" and the
Session variable is a "server key"]. Then, on every page, check that
the cookie and Session variable match.

Kudos
- to Joseph Shoe (Joe Hsu) for bringing this problem to the table
and
- to Tim for presenting tools and ways to manifest the problem
and to both of you for showing how to solve the problem:
I found no mention of session fixation attacks on the Microsoft
newsgroups prior to Joseph's. Nor could a quick search find anything
on Microsoft's site.

Here's a discussion, with diagrams, of the "session fixation
attack":
http://shiflett.org/articles/security-corner-feb2004

I am curious whether ASP.NET is vulnerable to this attack.

Google search shows that knowledge about such attacks has been
present since at least 2001.
http://www.tisc2001.com/newsletters/53.html
shows how a session fixation attack is set up [hint: the scenario
we've been discussing isn't the important one]. I don't believe that
this older paper explicitly considers the case of a legitimate user
who wishes to mimic another legitimate user and thereby gain
illegitimate access. And here's an update and PDF paper by the same
authors:
http://www.acrossecurity.com/papers.htm

Here's another article:
http://archives.neohapsis.com/archiv...2-q4/0117.html

IMO this "session fixation attack" is both interesting and a serious
problem for ASP applications. It seems especially pertinent to
intranets where secure information is maintained internally and
where security must not be breached. That is the most common
scenario for stealing information.

We need to talk about this more.