Penetration Testing mailing list archives
Re: --++[Preventing the spread of USB malware]++--
From: Shreyas Zare <shreyas () technitium com>
Date: Tue, 14 Apr 2009 23:52:09 +0530
Hi, I use a simpler solution. I format the USB drive with NTFS (you need to set the device policy as "optimize for performance" in hardware details for formatting with NTFS, after the format u can revert back to "optimize for quick removal" if you wish to). I configure the NTFS file permissions for the entire drive such that only my trusted machine users (the user a/c on machines I fully trust to be non infected) have write access, and Everyone user has only read & execute access. Remove all other users from the file permissions. Then the most important thing, create a folder which I generally name "DMZ" and set file permission Everyone Full Control. This folder thus can be accesses to save files on untrusted machines. Thus *only* this folder may contain infected files if used on infected machine. This idea makes creating "autorun.inf" files not possible unless the malware author write code to take ownership & change permissions (which I have not seen yet). So this works quite well and I have been using this without any issue since 1yr or so. On the side note, I am coding a application (which is in testing phase, and will be commercial soon) to tackle this problem effectively without doing any such things like formatting with NTFS or editing file table in HEX and would catch most malware that spread through USB. Regards, -- ("Computers have a strange habit of doing what you say, not what you mean." - SANS Top 25 Most Dangerous Programming Errors) Shreyas Zare Co-Founder, Technitium eMail: shreyas () technitium com ..::< The Technitium Team >::.. Visit us at www.technitium.com Contact us at theteam () technitium com Join Sci-Tech News group and get the latest science & technology news in your inbox. Visit http://tech.groups.yahoo.com/group/sci-tech-news to join. On Tue, Apr 14, 2009 at 5:36 PM, Marcus Vinicius <marcovvinicius () gmail com> wrote:
Hello guys. one nice text. //Author – Robin Bailey //Date – 05/04/2009 //Email - rbailey.security<0x40>googlemail.com //Contents [1] Introduction [2] The problem [3] Solution [4] Conclusion //Introduction [1] As the use of memory sticks has become more and more widespread, so malware has began to use them as a way to spread from machine to machine. While this is a problem for end users, the real danger is with IT professionals, who might use the same USB stick in dozens of computers in a single day, will often be logged in with administrative privileges, and will have access to important machines. This paper is aimed at those professionals, and how they can mitigate the risk of passing an infection onto other machines. //The Problem [2] Malware uses two main techniques to spread through memory sticks. The first, and less serious, is infecting executable files on the memory stick, so that when they are run on another machine, the infection moves with them. The more common, and more dangerous, is to spread via the `autorun.inf` file, which Windows automatically executes when the drive is connected, meaning that no user interaction is needed. Conficker has been getting a lot of attention recently, and this was one of the methods it used to spread itself, but many other malicious programs used the same technique. It is possible to disable the autorun feature from Windows, but this requires that the client machine has done this, which is not always the case, as most users will not have the technical knowledge to do this. //The Solution [3] Since we cannot rely on the computer to prevent the execution of the autorun.inf file, we must do this from the memory stick. It is possible to buy memory sticks with read-only switches, so that they can be locked to prevent the computer writing to them, but this can cause problems, is easily forgotten, and doesn't help once the memory stick has been infected. However, if the memory stick is FAT32, which most are, with the exception of some of the new 8GB+ drives, we can create a quick fix using a hex editor, and a basic knowledge of the FAT32 directory table. First, we create a blank `autorun.inf` file on the memory stick, then open up the disk in a hex editor. It doesn't matter if you open the physical disk, or the logical partition, but if the disk has more than one partition, it is better to do the latter. Make sure that the disk is opened with read/write permissions, and that you haven't got anything accessing it at the time. HxD for Windows is a small, portable hex editor, if you don't already have one. While this can be done to a disk with data on, it is safer to do it to a blank one, just in case there is a problem. If not, make sure that you have a copy of any data on the stick, if you don't, the you are liable to any loss of data that might occur. Next, run a search in the disk for the string `AUTORUN`, as a non-Unicode text string. It should find it near the beginning of the disk. The area we are interested in is as follows. 41 55 54 4F 52 55 4E 20 49 4E 46 20 A U T O R U N I N F The first 8 bytes are the filename (with a space at the end, because autorun is only 7 characters), followed by a 3 bytes file extension (INF), followed by one byte for the file attributes. It is this final byte that is relevant. The current value of the byte (0x20) has just the archive bit set. What we want to do, is to change this byte to 0x40, which sets the device bit, which is never normally found on a disk. The block will now look like this. 41 55 54 4F 52 55 4E 20 49 4E 46 40 A U T O R U N I N F @ Once this has been saved to disk, ignoring any warning that this might corrupt the disk, we then unmount and remount the volume. Now, when you browse to the disk, the autorun.inf file can be seen, but it cannot be deleted, opened, edited, overwritten, or have its attributes changed. When this memory stick is connected to an infected machine, which will try to create an autorun.inf file on it, it will fail with an error, (Cannot create file), meaning that this memory stick cannot be infected, and thus cannot pass an infection on to any other computers. //Conclusion [4] As stated before, this is not a guide aimed at end users, it is aimed at IT professionals, or other power users, who will use the same USB stick on multiple computers on a day to day basis. Should this technique become widely used, we will almost certainly see malware that can bypass it, but until that happens, it can provide a simple but effective defense against USB spreading malware. If you have any comments/questions/suggestions send me an email. # milw0rm.com [2009-04-06] # EOF -- LPIC-1 -- Linux Certified http://bi0os.blogspot.com "I like when the my box said: All ports Are filtred =:)"
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- --++[Preventing the spread of USB malware]++-- Marcus Vinicius (Apr 14)
- Re: --++[Preventing the spread of USB malware]++-- Shreyas Zare (Apr 14)
- Re: --++[Preventing the spread of USB malware]++-- Nathan Sportsman (Apr 15)
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- Re: --++[Preventing the spread of USB malware]++-- Marcus Vinicius (Apr 15)
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- Re: --++[Preventing the spread of USB malware]++-- Marcus Vinicius (Apr 15)
- Re: Botnets Aarón Mizrachi (Apr 03)
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- Re: --++[Preventing the spread of USB malware]++-- Shreyas Zare (Apr 15)
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- Re: --++[Preventing the spread of USB malware]++-- Shreyas Zare (Apr 16)
- Re: --++[Preventing the spread of USB malware]++-- Razi Shaban (Apr 14)
- Re: Botnets R. DuFresne (Apr 14)