[FD] Avast Virtualization Driver - Elevation Of Privileges

[Kyriakos Economou <keconomou@xxxxxxxxxxxxx>]

* CVE: CVE-2015-8620
* Vendor: Avast
* Reported by: Kyriakos Economou
* Date of Release: 17/02/2016
* Affected Products: Multiple
* Affected Version: <= v11.1.2245
* Fixed Version: v11.1.2253

Description:
A heap overflow bug in the Avast Virtualization kernel mode driver (aswSnx.sys) 
allows a local attacker to elevate his privileges from any account type and 
execute code as SYSTEM.


Affected Products:

Avast Internet Security v11.1.2245
Avast Pro Antivirus v11.1.2245
Avast Premier v11.1.2245
Avast Free Antivirus v11.1.2245

Earlier versions of these products are affected as well.


Technical Details:

The Avast virtualization kernel mode driver (aswSnx.sys) does not validate the 
length of absolute Unicode file paths in some of the IOCTL requests that 
receives from userland, which are later copied on fixed length paged pool 
memory  allocations.  This allows to corrupt a kernel object that the attacker 
controls, and execute code as SYSTEM.

Example:

kd> !pool a8f45816
Pool page a8f45816 region is Paged pool
a8f45000 size:  418 previous size:    0  (Allocated)  Dire (Protected) <--- 
object controlled by the attacker
a8f45418 size:  3b8 previous size:  418  (Free)       ....
*a8f457d0 size:  418 previous size:  3b8  (Allocated) *SnxN <--- attacker 
overflows this chunk
a8f45be8 size:  418 previous size:  418  (Allocated)  Dire (Protected) <--- 
object controlled by the attacker


Further reading: 
https://www.nettitude.co.uk/exploiting-a-kernel-paged-pool-buffer-overflow-in-avast-virtualization-driver

Disclosure Log:
Vendor Contacted: 23/12/2015
Public Disclosure: 17/02/2016

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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