Session Token Remains Valid After Logout in IBM Lotus Domino Web Access
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&uid=swg21245589
VI. CONTACT
You can reach the author of this advisory at:
dave.ferguson[at]fishnetsecurity(dot)com