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PUBLIC

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ACROS Security Problem Report #2010-04-12-1
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ASPR #2010-04-12-1: Remote Binary Planting in VMware Tools for Windows
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Document ID:     ASPR #2010-04-12-1-PUB
Vendor:          VMware, Inc. (https://www.vmware.com)
Target:          VMware Tools for Windows 
Impact:          Remote execution of arbitrary code on a virtual Windows
                 machine
Severity:        Very high
Status:          Official patch available, workarounds available
Discovered by:   Jure Skofic and Mitja Kolsek of ACROS Security

Current version 
   https://www.acrossecurity.com/aspr/ASPR-2010-04-12-1-PUB.txt


Summary
=======

A "binary planting" vulnerability in VMware Tools for Windows allows local 
or remote (possibly Internet-based) attackers to deploy and execute 
malicious code on virtual Windows machines in the context of logged-on 
users. 


Product Coverage
================

- VMware Tools for Windows build 91707
- VMware Tools for Windows version 7.8.4 build 126130
 
Note:  We only tested the above versions; other versions may also be 
affected. 


Analysis 
========

As a result of an incorrect dynamic link library loading in VMware Tools 
for Windows, an attacker can cause her malicious DLL to be loaded and 
executed from local drives, a remote Windows share, and even a share 
located on Internet. 

All a remote attacker has to do is plant a malicious DLL with a specific 
name on a network share and get the user to open any file from this 
network location with any Windows application - which should require 
minimal social engineering. Since Windows systems by default have the Web 
Client service running - which makes remote network shares accessible via 
WebDAV -, the malicious DLL can also be deployed from an Internet-based 
network share as long as the intermediate firewalls allow outbound HTTP 
traffic to the Internet. 

A systematic attack could deploy malicious code to a large number of 
virtual Windows workstations in a short period of time, possibly as an 
Internet worm.

Additional details are available to interested corporate and government 
customers under NDA, as public disclosure would reveal too many details on 
the vulnerability and unduly accelerate malicious exploitation.


Mitigating Factors 
==================

- A firewall blocking outbound WebDAV traffic (in addition to blocking all 
Windows Networking protocols) could stop an Internet-based attack.


Solution 
========

VMware has issued a security bulletin [1] and published remediated 
versions of VMware Workstation, Player, ACE, Server and Fusion, and 
patches for ESX and ESXi that fix this issue.

Warning: It is not enough to install the new version or the patch; it is 
also necessary to upgrade VMware Tools in each affected virtual machine. 
On VMware Workstation, Player, ACE, Server and Fusion, the user will be 
automatically prompted to upgrade, while there will be no such prompt on 
ESX and ESXi. The upgrade of VMware Tools requires a subsequent reboot of 
the virtual machine.


Workaround 
==========

- Stopping the Web Client service could stop Internet-based attacks 
as long as the network firewall stops outbound Microsoft Networking 
protocols. This would not, however, stop remote LAN-based attacks where 
the attacker is able to place a malicious DLL on a network share inside 
the target (e.g., corporate) network.

Other workarounds are available to interested corporate and government 
customers under NDA, as public disclosure would reveal too many details on 
the vulnerability and unduly accelerate malicious exploitation.


Related Services
================

ACROS is offering professional consulting on this issue to interested 
corporate and government customers. Typical questions we can help you 
answer are:

1) To what extent is your organization affected by this issue?

2) Is it possible to get remote code from the Internet launched inside 
   your network? Can this be demonstrated?

3) Have you adequately applied the remedies to remove the vulnerability?

4) Are there other workarounds that you could implement to fix this issue 
   more efficiently and/or inexpensively?

5) Are your systems or applications vulnerable to other similar issues?


Interested parties are encouraged to ask for more information at 
security@acrossecurity.com.
 

References
==========

[1] VMware Security Advisory VMSA-2010-0007 
    https://www.vmware.com/security/advisories/VMSA-2010-0007.html


Acknowledgments
===============

We would like to acknowledge VMware for professional handling of the 
identified vulnerability.


Contact
=======

ACROS d.o.o.
Makedonska ulica 113
SI - 2000 Maribor

e-mail: security@acrossecurity.com
web:    https://www.acrossecurity.com
phone:  +386 2 3000 280
fax:    +386 2 3000 282

ACROS Security PGP Key
   https://www.acrossecurity.com/pgpkey.asc
   [Fingerprint: FE9E 0CFB CE41 36B0 4720 C4F1 38A3 F7DD]

ACROS Security Advisories
   https://www.acrossecurity.com/advisories.htm

ACROS Security Papers
   https://www.acrossecurity.com/papers.htm

ASPR Notification and Publishing Policy
   https://www.acrossecurity.com/asprNotificationAndPublishingPolicy.htm


Disclaimer
==========

The content of this report is purely informational and meant only for the 
purpose of education and protection. ACROS d.o.o. shall in no event be 
liable for any damage whatsoever, direct or implied, arising from use or 
spread of this information. All identifiers (hostnames, IP addresses, 
company names, individual names etc.) used in examples and demonstrations 
are used only for explanatory purposes and have no connection with any 
real host, company or individual. In no event should it be assumed that 
use of these names means specific hosts, companies or individuals are 
vulnerable to any attacks nor does it mean that they consent to being used 
in any vulnerability tests. The use of information in this report is 
entirely at user's risk.


Revision History
================

April 12, 2010: Initial release


Copyright
=========

(c) 2010 ACROS d.o.o. Forwarding and publishing of this document is
permitted providing the content between "[BEGIN-ACROS-REPORT]" and
"[END-ACROS-REPORT]" marks remains unchanged.

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