Spammers use unicode trick to manipulate file names

Posted by   Virus Bulletin on   May 16, 2011

Windows executable appears to be Word document.

An unicode trick that reverses the order of some characters has been used by spammers to disguise malicious attachments as harmless file types.

Unicode enables the representation on computer screens of a very large and still growing number of alphabets, together with many special characters. Among this latter category are some 'characters' that reverse the order of the the visible characters. While this may be useful for some applications, it has now been abused by spammers to hide the file type of malicious attachments.

Security vendor Norman reports having seen some samples where a Chinese trojan - in this case a Windows executable - was attached to emails, with the .exe extension instead made to appear as .doc, making it look like a Word document. While Word documents may well contain malware themselves, they are less likely to trigger alarms than executables. The spammers must have expected some users to open them, thus infecting themselves with a nasty trojan.

As the special characters only alter the way the file is displayed, filters blocking executables are unlikely to be vulnerable from this kind of attack. Moreover, those Windows versions that are vulnerable (in the default settings only Vista and Windows 7), do display the file type correctly.

Nevertheless, this should be a warning to users that any kind of file has the potential to be malicious. And that basing one's trust on file extensions is a bad idea.

More at Norman's blog here, which also includes an example of how a screensaver can masquerade as a JPEG image.

Posted on 16 May 2011 by Virus Bulletin

twitter.png
fb.png
linkedin.png
hackernews.png
reddit.png

 

Latest posts:

New paper: Collector-stealer: a Russian origin credential and information extractor

In a new paper, F5 researchers Aditya K Sood and Rohit Chaturvedi present a 360 analysis of Collector-stealer, a Russian-origin credential and information extractor.

VB2021 localhost videos available on YouTube

VB has made all VB2021 localhost presentations available on the VB YouTube channel, so you can now watch - and share - any part of the conference freely and without registration.

VB2021 localhost is over, but the content is still available to view!

VB2021 localhost - VB's second virtual conference - took place last week, but you can still watch all the presentations.

VB2021 localhost call for last-minute papers

The call for last-minute papers for VB2021 localhost is now open. Submit before 20 August to have your paper considered for one of the slots reserved for 'hot' research!

New article: Run your malicious VBA macros anywhere!

Kurt Natvig explains how he recompiled malicious VBA macro code to valid harmless Python 3.x code.

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.