[TZO-15-2020] - F-SECURE Generic Malformed Container bypass (RAR)

Release mode    : Patch
Ref             : [TZO-15-2020] - F-SECURE Generic Malformed Container bypass (RAR)
Vendor          : F-SECURE
Status          : Patched
CVE             : none provided
Blog            : https://blog.zoller.lu
Vulnerability Dislosure Policy: https://caravelahq.com/b/policy/20949

Affected Products
=================
F-Secure Email and Server Security
F-Secure Internet GateKeeper
F-SECURE CLOUD PROTECTION FOR SALESFORCE

Linux below  17.0.605.474

I. Background
----------------------------
Quote: "Unprecedented challenges threaten to undermine the very survival of society. Only 
unprecedented innovation can prevent irreversible disasters. This is only possible if we 
trust the technology that can bring us together.

From our humble beginnings more than thirty years ago, F-Secure has grown into a reliable 
cyber security leader, earning the trust of organizations and people around the world."

II. Description
----------------------------
The parsing engine supports the RAR Archive. The parsing engine can be bypassed by specifically manipulating a RAR archive.


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
----------------------------
- For the unix version (IGK) the fix was released on 20th January with library version 17.0.605.474
- For Windows the version was already out in December 2019. There were also avira's fixes as well.

"We can conclude that January 20th date, since that is when the final fixes went out to production."

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

NOV 20 2019 - Report
DEC 20 2019 - Windows fixes released
JAN 20 2010 - Linux fix relesased