Cybersecurity researchers have uncovered a never-before-seen dropper that serves as a conduit to launch next-stage malware with the ultimate goal of infecting Windows systems with information stealers and loaders.
“This memory-only dropper decrypts and executes a PowerShell-based downloader,” Google-owned Mandiant said. “This PowerShell-based downloader is being tracked as PEAKLIGHT.”
Some of the malware strains distributed using this technique are Lumma Stealer, Hijack Loader (aka DOILoader, IDAT Loader, or SHADOWLADDER), and CryptBot, all of which are advertised under the malware-as-a-service (SaaS) model.
The starting point of the attack chain is a Windows shortcut (LNK) file that’s downloaded via drive-by download techniques — e.g., when users look up a movie on search engines. It’s worth pointing out that the LNK files are distributed within ZIP archives that are disguised as pirated movies.
The LNK file connects to a content delivery network (CDN) hosting an obfuscated memory-only JavaScript dropper. The dropper subsequently executes the PEAKLIGHT PowerShell downloader script on the host, which then reaches out to a command-and-control (C2) server to fetch additional payloads.
Mandiant said it identified different variations of the LNK files, some of which leverage asterisks (*) as wildcards to launch the legitimate mshta.exe binary to discreetly run malicious code (i.e., the dropper) retrieved from a remote server.
In a similar vein, the droppers have been found to embed both hex-encoded and Base64-encoded PowerShell payloads that are eventually unpacked to execute PEAKLIGHT, which is designed to deliver next-stage malware on a compromised system while simultaneously downloading a legitimate movie trailer, likely as a ruse.
“PEAKLIGHT is an obfuscated PowerShell-based downloader that is part of a multi-stage execution chain that checks for the presence of ZIP archives in hard-coded file paths,” Mandiant researchers Aaron Lee and Praveeth D’Souza said.
“If the archives do not exist, the downloader will reach out to a CDN site and download the remotely hosted archive file and save it to disk.”
The disclosure comes as Malwarebytes detailed a malvertising campaign that employs fraudulent Google Search ads for Slack, an enterprise communications platform, to direct users to phony websites hosting malicious installers that culminate in the deployment of a remote access trojan named SectopRAT.
