Avast SandBox Escape via IOCTL Requests

[Kyriakos Economou <keconomou () nettitude com>]

* CVE: CVE-2016-4025
* Vendor: Avast
* Reported by: Kyriakos Economou
* Date of Release: 19/04/2016
* Affected Products: Multiple
* Affected Version: Multiple
* Fixed Version: N/A


Description:
A design flaw in Avast Sandbox allows a potentially harmful program to escape the sandbox and infect the host by 
dropping its files out of it and/or by modifying existing legitimate files of any type.


Affected Products:

Avast Internet Security v11.x.x
Avast Pro Antivirus v11.x.x
Avast Premier v11.x.x
Avast Free Antivirus v11.x.x

Avast Business Security v11.x.x

Avast Endpoint Protection v8.x.x
Avast Endpoint Protection Plus v8.x.x
Avast Endpoint Protection Suite v8.x.x
Avast Endpoint Protection Suite Plus v8.x.x
Avast File Server Security v8.x.x
Avast Email Server Security v8.x.x

Earlier and latest versions of these products are currently affected.


Technical Details:
The Avast virtualization kernel mode driver (aswSnx.sys) handles specific IOCTL requests sent through the snxhk.dll 
module which is automatically loaded in the address space of all sandboxed processes. One of the features that this 
module attempts to provide, is to recognize user interaction with the GUI of the sandboxed application which 
facilitates saving a file out of the sandboxed process. For example, a user can still save a txt file out of a 
notepad.exe sandboxed process by navigating through the menu to the 'Save as' dialogue box of the application. The 
design flaw consists in the fact that there is no further authentication from the kernel driver itself with regards to 
the IOCTL requests, in order to verify that releasing a file out of the sandbox it is indeed an authorised action 
performed by the user. This vulnerability can be exploited by a malicious application in order to infect the host by 
dropping its files and/or  infect existing legitimate files of any type without requiring user interaction. A 
ransomware that exploits this vulnerability will be able to encrypt all the targetted files while its process will be  
running in the sandbox. This vulnerability is critical since it totally breaks the purpose of the Sandbox protection 
and other features, such as DeepScreen, that rely on this.


Further reading: https://www.nettitude.co.uk/escaping-avast-sandbox-using-single-ioctl-cve-2016-4025/

Disclosure Log:
Vendor Contacted: 01/11/2015
Request for Feedback: 23/11/2015
Request for Feedback: 01/04/2016
Public Disclosure: 19/04/2016

Copyright:
Copyright (c) Nettitude Limited 2016, All rights reserved worldwide.

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The information herein contained may change without notice. Any use of this information is at the user's risk and  
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from the use of this information.

Kyriakos Economou
Vulnerability Researcher

[logo]<http://www.nettitude.co.uk/>

P  +44 (0) 845 520 0085 ext 1189
F  +448455 200 222
keconomou () nettitude com<mailto:keconomou () nettitude com%0d>
www.nettitude.co.uk<http://www.nettitude.co.uk/>


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