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Netskope Threat Research Labs has identified a new malware named “ShortJSRAT” which uses a Windows script component scriptlet file with a .sct extension. The scripts we observed used cloud apps for delivering the next stage payloads. These payloads are executed using the “Squiblydoo” technique which use native windows applications to bypass application allow listing solutions like Windows Applocker. This solution allows only approved applications to load and execute. Additionally, threat actors behind this malware used various cloud applications to take advantage of a typical enterprise loopholes of bypassing security inspection for cloud application traffic. Netskope Threat Protection detects these scriptlets as Squiblydoo.ShortJSRAT.Gen1.
As part of our research efforts, we discovered multiple variants of ShortJSRAT malware using the Squiblydoo technique. This powerful technique used by threat actors uses various components such as trusted Microsoft binary, proxy, TLS encryption and webpage redirection allowing an attacker with normal privileges to download and execute a scriptlet from a remote host.Since, ShortJSRAT also downloads and executes scriptlets hosted on Cloud Apps, this makes traditional technologies which generally rely on static detections harder to detect and remediate the attack. One of the samples we discovered used Dropbox via Google URL shortener, while another sample used Google Storage APIs to download the scriptlet files. Another variant we discovered used Github as part of the attack kill chain along the lines of another interesting malware that we discovered recently which used Github for malware payload delivery. Based on our observation of ShortJSRAT using many cloud services for additional resiliency, enterprises need a CASB to efficiently analyze the unsanctioned stream context.
A typical delivery of ShortJSRAT and some of the attack kill chain phases are shown in Figure 1. A victim typically receives an email with a Google URL Shortener link and clicking on the link ultimately lead to the delivery of the ShortJSRAT malware.
Figure 1: Depiction of the ShortJSRAT attack kill chain
We identified ShortJSRAT as part of our monitoring efforts to identify new developments and evolution of CloudSquirrel and CloudFanta malware campaigns that we uncovered in 2016. Our investigation revealed similarities between ShortJSRAT scriptlet and some of the malware from CloudFanta campaign. The comparison of the code between CloudFanta malware and ShortJSRAT scriptlet is shown in Figure 2.
Figure 2: Comparison of CloudFanta and ShortJSRAT scriptlet
At this time we do not have enough evidence to claim that ShortJSRAT is the next version of CloudFanta.
As per our observation, ShortJSRAT is likely written or exclusively used by Brazilian threat actors. These threat actors use cloud services to download and deliver the malware and its payloads via a portable executable file ( like DLL and EXE ) with a “.png” extension. There were also some variants that downloaded 32-bit or 64-bit executables with a check of file path “c:\\Program Files (x86)” to determine if the victim is using a 32-bit or 64-bit operating system.
Netskope Threat Detection and Protection
Netskope Threat Protection detects these scriptlets as Squiblydoo.ShortJSRAT.Gen1. Additionally, Netskope customers can enable cloud app instance-level policies to block downloads from unsanctioned cloud storage applications while allowing full access to enterprise sanctioned instances. This can aid Netskope customers in preventing this attack with app instance-level granularity. Applying such policies ena