Title:
======
AVAST Antivirus v8.0.1489 - Multiple Core Vulnerabilities


Date:
=====
2013-06-30


References:
===========
http://www.vulnerability-lab.com/get_content.php?id=963


VL-ID:
=====
963


Common Vulnerability Scoring System:
====================================
4.1


Introduction:
=============
Avast! (styled avast!) is - both freeware and payable - an antivirus computer program with user interface that includes 41 languages, 
available to Microsoft Windows, Mac OS X and Linux users. The name Avast is an acronym of `Anti-Virus – Advanced Set`. The official, 
and current logo of Avast! is a white orb with the letter `a` on it and an orange circle around it, sticking out to four directions.
Its developer, AVAST Software a.s. (formerly known as ALWIL Software a.s.), has headquartered in Prague, Czech Republic, with offices 
in Linz, Austria; Friedrichshafen, Germany; and San Mateo, California.

It has been awarded VB100 Award by Virus Bulletin multiple times for 100% detection of `in-the-wild` viruses, and also won the Secure 
Computing Readers`Trust Award. The central scanning engine has been certified by ICSA Labs and West Coast Labs` Checkmark process.
Avast! competes in the antivirus industry against Avira, AVG Technologies, Bitdefender, F-Secure, Frisk, Kaspersky, McAfee, Symantec 
and Trend Micro among others.

(Copy of the Homepage: http://en.wikipedia.org/wiki/Avast! )


Abstract:
=========
The Vulnerability Laboratory Research Team discovered a persistent code execution and local command path injection vulnerability 
in the free AVAST Antivirus v8.0.1489 software.



Report-Timeline:
================
2013-06-06: Researcher Notification & Coordination (Ateeq Khan)
2013-06-07: Vendor Notification (AVAST! - Security Incident Team)
2013-06-09: Vendor Response/Feedback (AVAST! - Security Incident Team)
2013-**-**: Vendor Fix/Patch (AVAST! - Developer Team)
2013-06-30: Public Disclosure (Vulnerability Laboratory)



Status:
========
Published


Affected Products:
==================
AVAST!
Product: Antivirus 8.0.1489


Exploitation-Technique:
=======================
Local


Severity:
=========
Medium


Details:
========
It has been discovered that the lastest build of Avast Free Antivirus Version 8 is vulnerable to HTML code injection 
which eventually leads to local command / shell execution. During the testing, I was able to succesfully bypass the 
AVAST Sandbox and read/load and execute any file/application from local system having the local admin priviledges 
which makes this bug alot more critical. 

Initially the bug was an HTML code injection flaw only however, with more indepth analysis, it was revealed that the 
severity of this vulnerability is far more critical. A simple <a href> tag bypasses the AVAST Sandbox and drops a 
locall CMD shell on the system where AVAST is installed. You can technically access any file / application, execute it. 
It seems like We can control explorer.exe and through that we are even able to browse local folders and access any file, 
we can even browse external websites.

The bug exists in the Maintenance / Registration Module under the Offline Registration Section in the `Insert the License Key` field. 
Since proper input sanatization is not being performed, a user can insert any HTML code which then gets executed successfully. For a 
POC i used the <img> and <a href> tags to read/load and execute files from my local system. I believe there may be possibilities of 
multiple attack vectors keeping in mind the scope of this vulnerability.

During the POC, I was able to successfully bypass the AVAST sandbox and I was able to run local system level commands using the AVAST Interface.

These sort of vulnerabilities can result in multiple attack vectors on the clients end which may eventually result in complete compromise of the 
end user system. This code injection vulnerability exists in the main core AVAST Antivirus application.

Exploitation of this vulnerability requires a low or medium user interaction. Successful exploitation of the vulnerability may result in malicious 
script code being executed resulting in local command/shell injection, persistent phishing, Client side redirects and similar dangerous attacks.

Vulnerable Product(s):
        [+] Avast Free Antivirus Version 8 - Latest Release 

Vulnerable Section(s):
        [+] Offline Registration

Vulnerable Module(s):
        [+] Registration Information (Maintainence)

Vulnerable Input Field(s):
        [+] License Key  


Proof of Concept:
=================
Proof of Concept #1 HTML Code Injection

For reproducing the HTML Code Injection bug successfully, please follow the below mentioned steps:

a) Download / Install the Latest Version of Avast Free Antivirus 8
b) After installation, Right Click on Avast Tray Icon and click on ``Registration Information``
c) Scroll down to the `Offline Registration` section and click on ``Enter the License Key``
d) Enter the following payload <h1>Vulnerable</h1> and click OK
e) You should now see the entered string `Vulnerable` in Heading 1 format proving the existence of this vulnerability.



Proof of Concept #2 Local Image File Include

For reproducing the Local File include through <img> tag bug successfully, please follow the below mentioned steps:

a) Right Click on Avast Tray Icon and click on ``Registration Information``
b) Scroll down to the `Offline Registration` section and click on ``Enter the License Key``
c) Enter the following payload <img src=``file:///YOURFILE``></img> and click OK
d) You should now see the local image file loaded successfully from your system proving the existence of this vulnerability.

Note:
For POC #2 I copied a file called logo.png to my C:/ folder and used the following payload to produce the bug <img src=``file:///C:/logo.png``></img>



Proof of Concept #3 Command Shell on Local System (cmd.exe)

For reproducing the bug, please follow these below mentioned steps:

a) Right Click on Avast Tray Icon and click on ``Registration Information``
b) Scroll down to the `Offline Registration` section and click on ``Enter the License Key``
c) Enter the following payload <a href=``cmd``> and click OK
d) You should now see the cmd.exe file loaded successfully from your system proving the existence of this vulnerability.
e) You can also use the payloads mentioned under next section for some interesting results:


Interesting Payloads:

<a href=``test.com``>
<a href=``explorer.exe``>
<a href=````>
<a href=``shell:System``>
<a href=``calc``>
<a href=``mspaint.exe``>
<a href=``notepad.exe``>

Please note: All tests were performed on a system running latest version of MicroSoft Windows 7 OS.


POC Technical Description 
Here, we used the common HTML tags as our payload. The fact that user injected HTML code is being executed succesfully raises concerns for this core applications security. Then, the fact that using just the <a href> tag, we can easily bypass AVAST Sandbox and gain local system shell with priviledges of the user that installed the application initially which in most cases will be administrator is very critical. I believe this bug can be further escalated to gain more interested results. I also wanted to test the License file for input validation but I havent been able to perform that test yet due to not having access to a proper license file. I intend to test that feature because i believe it might also be vulnerable.


Solution:
=========
By default, no user should be allowed to inject HTML code in the application. This can be mitigated by performing proper input sanatization 
of the vulnerable fields. All illegal characters should also be escaped and application source code should be hardened overall. 
Proper input sanatization in the source code will fix this issue.



Risk:
=====
The security risk of the detected software vulnerabilities are estimated as medium(+).



Credits:
========
Vulnerability Laboratory [Research Team] - Ateeq Khan [ateek@vulnerability-lab.com]


Disclaimer:
===========
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