Paper: The Hulk

Posted by   Virus Bulletin on   Oct 8, 2014

Raul Alvarez studies cavity file infector.

Most file infectors increase the length of the infected file, as the malicious code is added as a new section of the host file, or to the last section of that file. 'Cavity' file infectors are different though: they infect files without increasing their size.

Today, we publish a paper by Raul Alvarez, a researcher for Fortinet, in which he studies Win32/Huhk, a virus that implements cavity file infection.

In the paper, Raul explains what happens when an infected file is run, as well as how other files are being infected. Huhk is polymorphic in nature, something which is achieved through a simple XOR operation with a one-byte key.

Of course, the virus needs to find a way to hide in the host file without affecting the latter's ability to run. To this end, Huhk looks for continuous memory locations filled with zeros. If the total size of such locations is greater than 7,005 bytes, it is able to infect the file.

You can read the paper here in HTML format or here as a PDF.

If you like this paper, you will probably like two other papers by Raul we published recently: Bird's Nest (on Neshta) and API-EPO (on W32/Daum).

Posted on 08 October 2014 by Martijn Grooten



Latest posts:

Nominations opened for sixth Péter Szőr Award

Virus Bulletin is seeking nominations for the sixth annual Péter Szőr Award.

Haroon Meer and Adrian Sanabria to deliver VB2019 closing keynote

New additions to the VB2019 conference programme include a closing keynote address from Thinkst duo Haroon Meer and Adrian Sanabria and a talk on attacks against payment systems.

Free VB2019 tickets for students

Virus Bulletin is excited to announce that, thanks to generous sponsorship from Google Android, we are able to offer 20 free tickets to students who want to attend VB2019.

VB2018 paper: Lazarus Group: a mahjong game played with different sets of tiles

The Lazarus Group, generally linked to the North Korean government, is one of the most notorious threat groups seen in recent years. At VB2018 ESET researchers Peter Kálnai and Michal Poslušný presented a paper looking at the group's various…

Book your VB2019 ticket now for a chance to win a ticket for BSides London

Virus Bulletin is proud to sponsor this year's BSides London conference, which will take place next week, and we have a number of tickets to give away.

We have placed cookies on your device in order to improve the functionality of this site, as outlined in our cookies policy. However, you may delete and block all cookies from this site and your use of the site will be unaffected. By continuing to browse this site, you are agreeing to Virus Bulletin's use of data as outlined in our privacy policy.