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:

Paper: Alternative communication channel over NTP

In a new paper published today, independent researcher Nikolaos Tsapakis writes about the possibilities of malware using NTP as a covert communication channel and how to stop this.

VB2019 conference programme announced

VB is excited to reveal the details of an interesting and diverse programme for VB2019, the 29th Virus Bulletin International Conference, which takes place 2-4 October in London, UK.

VB2018 paper: Under the hood - the automotive challenge

Car hacking has become a hot subject in recent years, and at VB2018 in Montreal, Argus Cyber Security's Inbar Raz presented a paper that provides an introduction to the subject, looking at the complex problem, examples of car hacks, and the…

VB2018 paper and video: Android app deobfuscation using static-dynamic cooperation

Static analysis and dynamic analysis each have their shortcomings as methods for analysing potentially malicious files. Today, we publish a VB2018 paper by Check Point researchers Yoni Moses and Yaniv Mordekhay, in which they describe a method that…

VB2019 call for papers closes this weekend

The call for papers for VB2019 closes on 17 March, and while we've already received many great submissions, we still want more!

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.