Message-ID: <042f9470-752c-a519-aa1e-6eecbdbd81f0@zoller.lu>
Date: Thu, 2 Jan 2020 16:21:39 +0100
From: Thierry Zoller <thierry@...ler.lu>
To: fulldisclosure@...lists.org
Subject: [FD] [TZO-03-2020] ESET Generic Malformed Archive Bypass (ZIP
 Compression Information)


________________________________________________________________________

                 From the low-hanging-fruit-department
   ESET Generic Malformed Archive Bypass (ZIP Compression Information)
________________________________________________________________________

Release mode    : Coordinated Disclosure
Ref             : [TZO-03-2020] - ESET Generic Malformed Archive Bypass 
(ZIP Compression Information)
Vendor          : ESET
Status          : Patched
CVE             : Unknown
Dislosure Policy: https://caravelahq.com/b/policy/20949
Blog            : https://blog.zoller.lu
Vendor Advisory : https://support.eset.com/en/modules-review-november-2019


Introduction
============
10 years ago I took a look at ways to evade AV/DLP Engine detection by 
using various techniques and released a metric ton of Advisories. 10 
years later after multiple CISO type roles I wanted to deep dive again 
and see how far (or not) the AV  industry has reacted to this class of 
vulnerabilities.

These types of evasions are now actively being used in offensive 
operations [1]. To my surprise with a few exceptions most AV Vendors 
haven't, in some cases I found the very same vulnerabilities that were 
patched and disclosed years ago.

Worse than that is the fact that some vendors that were very 
collaborative in 2008/2009 have now  started to ignore submissions 
(until I threaten disclosure) or are trying to argue that generically 
evading AV detection is not a vulnerability.

A lot of exchanges took place on this matter, for instance one vendor 
argued that this could not be called a vulnerability because it would 
not impact Integrity, Availability or Confidentiality so it can't 
possible be a vulnerability.

Even more bothering to me is how the bu bounty platform have created a 
distorted Reporter/Vendor relationship and mostly are executed to the 
detriment of the customers. I am collecting my experiences and will 
write a blog post about this phenomnon.

There will by many more advisories, hoping that I can finally erradicate 
this bug class and I don't have to come back to this 10 years from now 
again.

[1] 
https://www.bleepingcomputer.com/news/security/specially-crafted-zip-files-used-to-bypass-secure-email-gateways/
https://www.techradar.com/news/zip-files-are-being-used-to-bypass-security-gateways


Affected Products
=================
All below version v. 1294

ESET Smart Security Premium
ESET Internet Security
ESET NOD32 Antivirus
ESET Cyber Security Pro (MAC)
ESET Cyber Security (MAC)
ESET Mobile Security for Android
ESET Smart TV Security
ESET NOD32 Antivirus 4 for Linux Desktop


I. Background
----------------------------
"For three decades we've been helping people to protect their digital 
worlds. From a small,  dynamic company we've grown into a global brand 
with over 110 million users in 202 countries
and territories. Many things have changed, but our core aspirations, 
philosophy and values remain the same – to help build a more secure 
digital world where everyone can truly Enjoy Safer Technology."

II. Description
----------------------------
The parsing engine supports the ZIP archive format. The parsing engine 
can be bypassed  by specifically manipulating an ZIP Archive Compression 
Information Field so that it can be accessed by an end-user but not the 
Anti-Virus software. The AV engine is unable to scan the container and 
gives the file a "clean" rating.

I may release further details after all known vulnerable vendors have 
patched their products.


III. Impact
----------------------------
Impacts depends on the contextual use of the product and engine within 
the organisationof a customer. Gateway Products (Email, HTTP Proxy etc) 
may allow the file through unscannedand give it a clean bill of health. 
Server side AV software will not be able to discoverany code or sample 
contained within this ZIP 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 implantsor 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
----------------------------
Reported submissions were fixed in new version (v. 1294) of unpacker 
module with following release schedule:
30.10.2019 - pre-release
4.11.2019 - final release


Thanks to ESET for their customer focused approach to coordinating this 
vulnerability.


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