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Update August 31, 2017: Netskope Threat Research Labs has spotted that Locky variant LUKITUS now using 7Z format for email attachments. It uses simple names for attachment like documents.7z, photos.7z, scans.7z. The attachment contains malicious VBS script code which downloads Locky Ransomware and encrypts user files with “.LUKITUS” extensions as detailed in our recent blog. Netskope Threat Protection detects the VBS archived in the 7zip as “vb:trojan.agnt.cmbk” and the payload as “Win32:Trojan:Locky:L”.
Last year, Netskope Threat Research Labs blogged about various evolution stages of the popular Locky Ransomware namely usage of cloud apps, usage of DLL (Dynamic Link Library) instead of EXE (Executable File) and usage of “.AESIR” and “.ZZZZZ” extensions for encrypted files. Netskope Threat Research Labs has constantly been tracking campaigns related to Locky, which after remaining passive in last couple months has emerged with a massive ongoing email campaign. The emails are sent with zip file as an attachment. The zip file contains malicious VBScript or JavaScript which act as downloader for Locky variant Ransomware. The Ransomware on execution encrypts the files using a new extension “.LUKITUS”. Netskope Threat Protection detects the malicious VBS and JS files as Backdoor.js.ryw and Backdoor.JS.agnt.qvs respectively. The blog provides more details about the workings of the malware.
Analysis of VBScript and JavaScript files
As mentioned earlier, this variant of Locky spreads either via VBScript or JavaScript file bundled inside ZIP archives as attachments. Both format of the scripts are obfuscated. For example of one of the malicious VBScript code we analyzed is shown in Figure 1.
Figure 1: Malicious VBScript code
On the same lines, an example of one of the JavaScript code we analyzed is shown in Figure 2.
