In our 2013 Security Predictions, we anticipated that cybercriminals would focus on refining existing tools, instead of creating new threats. Two threats that both represent refinements of previously known threats show this effectively.
CryptoLocker: Latest Ransomware Wave
Aside from using freebies, contests, or spoofing popular brands, cybercriminals can use other, similarly effective lures from their social engineering toolbox. This includes intimidating or even downright scaring users to coax them into purchasing bogus products or just giving away their data or money. Such tactic is obviously manifested in threats like FAKEAV and now, ransomware.
Earlier, ransomware had taken a new form – namely, police Trojans. These malware typically block access to the system and show a spoofed local enforcement agency notice to users. This accuses the victims of doing something illegal on the Internet and that they should pay a fine.
However, the latest ransomware variants (known as cryptolockers) now encrypt files besides locking the system. This is to ensure that users will still pay up even if the malware itself was deleted. A recent cryptolocker (detected as TROJ_CRILOCK.AE) also displays a wallpaper with a warning to users. The warning tells users that even if they delete the malware from their system, the encrypted files will remain inaccessible.
The private key which supposedly unlocks the encrypted file will be deleted should users choose not to purchase this key for $300 (or 300 euro). Apart from this routine, this malware shows similar routines to other reported cryptolock variants.
How to Keep a Low Profile, SHOTODOR style
Another way to make an attack successful is to remain unnoticed by users and even antimalware software. We’ve encountered BKDR_SHOTODOR.A which use garbage code and randomly named files to take obfuscation to the next level. (Note that the perpetrators of this attack are completely different from the previous one.)
Currently, the infection vector is yet to be determined. Based on our analysis, the threat starts with a dropper component, which drops multiple files onto the affected system. Looking closely into these files, most files contain some numeric values, while other files contain data that is harmless. However, one file stands out because of its large file size. It also contains numeric “garbage” strings. In reality, these codes hide the actual malicious code, which is an obfuscated AutoIt script.
The question then is, how will the malicious code be executed? One of the dropped files contains an AutoIt script interpreter that loads the obfuscated script mentioned earlier. Once done, it triggers the said script to build the rest of malicious codes by collecting the information in the other dropped files. In doing so, this code creates an executable file in the memory and inject it in a normal process. This malicious executable performs the backdoor routines (e.g. communicating to C&C server, executing of malicious commands etc.).
By opting to “disperse” the malicious code and building them afterwards to create a malicious executable file, the threat actors are obviously attempting to prevent detection and remain hidden. All the related files are detected by Trend Micro as BKDR_SHOTODOR.A.
These threats highlight how instead of attackers creating completely new kinds of threats, attackers are opting to modify existing threats which are still effective. While not completely “new”, they still pose a significant threat to users today.
To protect your systems from this threat, always observe best computing practices such as avoiding visiting unverified sites, clicking links from unknown sources, and avoiding executing/opening attachments from dubious email messages. Trend Micro protects users from this threat by detecting the malware cited in this blog.
With additional analysis from Alvin Bacani and Lenart Bermejo.