[TZO-11-2020] - ESET Generic Malformed Archive Bypass (BZ2 Checksum) Feb 13 2020 12:44PM
Thierry Zoller (thierry zoller lu)

From the low-hanging-fruit-department
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 : Unknown
Dislosure Policy: https://caravelahq.com/b/policy/20949
Blog :
Vendor Advisory : https://support.eset.com/en/modules-review-november-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 â?? 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 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

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

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