New PEAKLIGHT Dropper Deployed in Attacks Targeting Windows with Malicious Movie Downloads

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.”

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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.

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