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.