[FD] Avast SandBox Escape via IOCTL Requests

[Kyriakos Economou <keconomou@xxxxxxxxxxxxx>]

* 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:
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Kyriakos Economou
Vulnerability Researcher

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F  +448455 200 222
keconomou@xxxxxxxxxxxxx<mailto:keconomou@xxxxxxxxxxxxx%0d>
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