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List:       full-disclosure
Subject:    [FD] [TZO-16-2020] - F-SECURE Generic Malformed Container bypass (GZIP)
From:       Thierry Zoller <thierry () zoller ! lu>
Date:       2020-02-24 9:38:50
Message-ID: 8b54bb92-6402-96b8-8a8f-b2300c5366b8 () zoller ! lu
[Download RAW message or body]

________________________________________________________________________

                 From the low-hanging-fruit-department
	F-SECURE Generic Malformed Container bypass (GZIP)
________________________________________________________________________

Ref             : [TZO-16-2020] - F-SECURE Generic Malformed Container 
bypass (GZIP)
Vendor          : F-SECURE
Status          : Patched
CVE             : CVE-2020-9342
Blog            : 
https://blog.zoller.lu/p/tzo-16-2020-f-secure-generic-malformed.html
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 GZIP Archive. The parsing engine can be 
bypassed by manipulating a GZIP archive (Compression Method). This way 
the User can extract the file but the AV Engine cannot giving the file a 
clean pass.


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
----------------------------

We would like to thank F-Secure for their customer oriented way of 
handling this vulnerability.

- NOV 14 2019
Initiated Vulnerability coordination

- FEB 05 2020
F-Secure notifies me that they have patched the flaw.


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