[TZO-19-2020] - AVIRA Generic AV Bypass (ISO Container)

Release mode    : Coordinated Disclosure
Ref             : [TZO-19-2020] - AVIRA Generic AV Bypass (ISO Container)
Vendor          : AVIRA
Status          : PATCHED - Engine version 8.3.54.138.
CVE             : none provided,
Blog            : https://blog.zoller.lu
Vulnerability Dislosure Policy: https://caravelahq.com/b/policy/20949

Affected Products
=================
AV Engine below 8.3.54.138

All Avira products : 
- Avira Antivirus Server
- Avira Antivirus for Endpoint
- Avira Antivirus for Small Business
- Avira Exchange Security (Gateway)
- Avira Internet Security Suite for Windows
- Avira Prime
- Avira Free Security Suite for Windows
- Cross Platform Anti-malware SDK

Attention:
Avira does not patch or update their very popular command line scanner that is still available for download on their website. Since Avira does not release and advisory their customers are none the wiser.

Avira licenses it's engine to many OEM Partners. The OEM Partners that use the Avira Engine may be vulnerable or not. I would advise that you reach out to the vendors listed below to know whether you are affected or not. OEM Partners
can reach out to me to retreive the POC in order to test.

AVIRA OEM Partners:
- F-Secure
- Sophos
- Barracude
- Alibaba Cloud Security
- Check Point
- CUJO AI
- TP-Link
- FujiSoft
- AWS
- Rohde and Schwarz
- Careerbuilder
- Huawei
- Dracoon
- Total Availability
- FixMeStick
- APPVISORY
- Tabidus
- Cyren


Source : 
https://oem.avira.com/en/partnership/our-partners


I. Background
----------------------------
Quote: "We protect people—like you—across all devices, both directly and via our OEM partnerships.We provide a wide variety of best-in-class solutions to enhance your protection, performance, 
and online privacy—ranging from antivirus to VPN and cleanup technologies.

A server security should get special attention, as a single employee might store a malicious file on the network and instantly cause a cascading damage across the entire organization. 
With Avira's solutions for server security you can prevent such scenarios by protecting your network, data, and web traffic. "

Avira has the Trust Seal or the 
http://www.teletrust.de/itsmig/


II. Description
----------------------------
The parsing engine supports the ISO container format. The parsing engine can be bypassed  by specifically manipulating the ISO Archive
This leads to the Endpoint ignoring the container and the Gateways to let this file slip through uninspected.


III. Impact
----------------------------
It bypasses Avira perimeter defenses and sheduled AV scans.

Impacts depends on the contextual use of the product and engine within the organisation
of a customer. Gateway Products (Email, HTTP Proxy etc) may allow the file through unscanned
and give it a clean bill of health. Server side AV software will not be able to discover
any code or sample contained within this ISO file and it will not raise suspicion even 
if you know exactly what you are looking for (Which is for example great to hide your implants
or Exfiltration/Pivot Server).

There is a lot more to be said about this bug class, so rather than bore you with it in
this advisory I provide a link to my 2009 blog post 
http://blog.zoller.lu/2009/04/case-for-av-bypassesevasions.html

IV. Patch / Advisory
----------------------------
PATCHED - Engine version 8.3.54.138.

V. Disclosure timeline
----------------------------

How Avira handled these reports in 2009 :
https://blog.zoller.lu/2009/04/avira-antivir-generic-cab-bypass.html

28 NOV 2019
Submitted the Vulnerabiltiy Details

04 DEC 2019
AVIRA releases a patch