[TZO-11-2020] - ESET Generic Malformed Archive Bypass (BZ2 Checksum)

Release mode    : Coordinated Disclosure
Ref             : [TZO-11-2020] - ESET Generic Malformed Archive Bypass (BZ2 Checksum)
Vendor          : ESET
Status          : Patched 
CVE             : CVE-2020-10180
Dislosure Policy: https://caravelahq.com/b/policy/20949
Blog            : https://blog.zoller.lu
Vendor Advisory : https://support.eset.com/en/ca7387-modules-review-december-2019



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 BZ2 archive format. The parsing engine can be bypassed
by specifically manipulating an BZ2 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 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
----------------------------
Reported submissions were fixed in new version (v. 1296) of unpacker module


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