Date: Tue, 12 Sep 2006 12:47:38 -0500
From: "Ferguson, David" <Dave.Ferguson@...hnetsecurity.com>
To: <full-disclosure@...ts.grok.org.uk>
Subject: RE: Session Token Remains Valid After Logout in IBM
	Lotus Domino Web Access

Trey,
I understand what you mean about a design trade-off.  In this case I believe IBM has a conflicting
design.  They clear the cookie, which makes the user appear to be logged out of all applications.
However, they leave the token valid on the server, which doesn't serve any useful purpose.
-Dave
 
  _____  

From: Trey Keifer [mailto:midnitrcr@...il.com] 
Sent: Tuesday, September 12, 2006 11:34 AM
To: Ferguson, David
Subject: Re: [Full-disclosure] Session Token Remains Valid After Logout in IBM Lotus Domino Web Access
 
> The problem I see is that the user explicitly chose to log out.

The issue is when it comes to SSO, you don't know if the user wanted to log out of *that* application
or *all applications* and that is the "design tradeoff" I mentioned in my response. Some vendors
choose to invalidate all sessions, some make attempts to invalidate the specific instances. It is
against best-practices in single-instance application design, but it is an immutable logic problem in
SSO application design. The app can't guess what the user intends to do. 
On 9/12/06, Ferguson, David wrote: 
The problem I see is that the user explicitly chose to log out.  I have tested other SSO applications
where if you log out of the application, then the token is invalidated and you become unauthenticated
in all of the apps that are part of the SSO group.  To me that is the correct behavior.  In fact I
would say that IBM agrees with that, because their software goes to some extent to delete the cookie
from the browser so that if the user tries to access any of the apps after logging out, he is given a
login page to re-authenticate.  IBM believes it is valid and has released a technote
(http://www-1.ibm.com/support/docview.wss?rs=463
<http://www-1.ibm.com/support/docview.wss?rs=463&uid=swg21245589> &uid=swg21245589 ) on the subject.
 
Dave
 
  _____  

From: Trey Keifer [mailto:midnitrcr@...il.com] 
Sent: Tuesday, September 12, 2006 10:58 AM
To: Ferguson, David
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: [Full-disclosure] Session Token Remains Valid After Logout in IBM Lotus Domino Web Access
 
How is this a vulnerability? this is a common design trade-off of SSO tokens. In order to support the
user opening and closing multiple applications and not requiring them to login again to individual
applications (which is the point of SSO) they must invalidate the token in specific instances while
leaving a more encompassing SSO token valid until a defined timeout. 

You also say you didn't test the difference between SSO mode and "Single Server" mode. It seems to me
that this would be a key test, is it possible that this functionality *does* change when the server
knows it does not have to worry about session management across multiple instances? 

Furthermore, this alert requires access to the token (which we are left to make assumptions about
since no details on length or algorithm were included) which, unless the application only supports
HTTP, is a pretty obvious issue and not even worth reporting. If we include web applications that
don't invalidate sessions on the server side as reportable instances of vulnerabilities, then we open
the flood-gates for worthless advisories. 
On 9/12/06, Ferguson, David < Dave.Ferguson@...hnetsecurity.com
<mailto:Dave.Ferguson@...hnetsecurity.com> > wrote:
I. SYNOPSIS

Title: Session Token Remains Valid After Logout in IBM Lotus Domino Web Access 7.0.1
Release Date: 09/12/2006
Affected Application: IBM Lotus Domino Web Access 7.0.1
(versions prior to 7.0.1 were not tested but may still be vulnerable). 

Nominal Severity: Low
Severity If Successfully Exploited: High
Impact: Attacker impersonates legitimate user
Mitigating Factors: Requires discovery of a valid LtpaToken to exploit.

Discovery: Dave Ferguson, Security Consultant, FishNet Security 
Initial Notification of Vendor: 08/28/2006
Permanent Advisory Location:
http://www.fishnetsecurity.com/csirt/disclosure/ibm

II. EXECUTIVE SUMMARY 

Vulnerability Overview:

In Lotus Domino Web Access (DWA) 7.0.1, the session token used to identify the user (called
"LtpaToken") is not invalidated on the server upon user logout.  The cookie is removed from the 
browser, but the token continues to be recognized by the server until a configurable expiration time
is reached.

Attack Overview:

The most likely attack scenario is session hijacking or session stealing.  Knowing a valid session 
token would allow a malicious person to access all functionality of the web application (except
changing password, which requires knowledge of the current password).  Lotus DWA is a personal
information management application that includes e-mail, calendar, and task management.  By hijacking 
(or stealing) a session, an attacker is able to impersonate a legitimate user, and can read the user's
e-mail, send e-mail as the user, or change the user's preference settings.

III. TECHNICAL DETAIL

Vulnerability Details:

When a Lotus DWA user logs in, a cookie called "LtpaToken" is set into the browser and is used
throughout the session to uniquely identify the user.  When a user logs out of DWA, the cookie is 
cleared from the browser, but this action has no effect on the server.  The token eventually expires
on the server after some configurable amount of time.  A user who explicitly logs out of DWA may have
a false sense of security.  The LtpaToken cookie in his browser is deleted, but the token is still 
valid from the server's perspective and can be used by an attacker if he can discover it.  Best
practices in web application security would call for the LtpaToken to be invalidated/destroyed at
logout time.  Note that the vulnerability described here was observed with Session authentication 
under the Domino Web Engine tab set to "Multiple Servers (SSO)".  The same behavior may occur with the
"Single Server" configuration as well, but this was not tested.

The "LtpaToken" described here is a component in IBM's Lightweight Third-Party Authentication (LTPA) 
technology.  The LTPA technology was designed to be a defacto standard across the IBM product family.
LTPA is used in both IBM WebSphere and Lotus Domino products and allows for single sign-on across
physical servers.  For example, Domino can recognize and accept LTPA tokens created by WebSphere.  For

more information, please see the IBM redpaper at
http://www.redbooks.ibm.com/redpieces/pdfs/redp4104.pdf

IV. MITIGATING FACTORS

Keeping the LtpaToken confidential is critical to mitigating this issue.  An attacker must be able to 
discover a valid LtpaToken before it expires.  Because the LtpaToken is sent with each request, Lotus
DWA should be deployed as a secure application.  This means an SSL certificate should be installed on
the server so that encrypted (https) communication between the browser and the server occurs. 

Cross-site scripting (XSS) is a common application-level attack that can be used to steal cookies such
as LtpaToken.  Running the application under SSL does not hinder XSS attacks.  Fortunately, Lotus
Domino includes a module called Active Content Filter that is highly effective at removing potentially

harmful scripts in e-mail messages.  Active Content Filtering should be turned on.

Finally, the overall risk level can be lowered by enabling an idle session timeout in addition to the
absolute expiration time.  Ideally, from an application security perspective, the idle (inactivity) 
timeout would be much smaller than the absolute expiration.  Be aware that the increased security from
having small timeout values may negatively affect end-user satisfaction in the application.

V. VENDOR RECOMMENDED ACTIONS 

IBM recommends running Lotus DWA run under SSL and using a token expiration time of 30 minutes.

Please see IBM technote #1245589:
http://www-1.ibm.com/support/docview.wss?rs=463
<http://www-1.ibm.com/support/docview.wss?rs=463&uid=swg21245589> &uid=swg21245589 

VI. CONTACT

You can reach the author of this advisory at: dave.ferguson[at]fishnetsecurity(dot)com

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