As part of multiple campaigns detected by cybersecurity firm SentinelOne, a new AdLoad malware strain is infecting Macs bypassing Apple's YARA signature-based XProtect built-in antivirus. 

AdLoad is a widespread trojan that has been aiming at the macOS platform since late 2017 and is used to distribute a variety of malicious payloads, including adware and Potentially Unwanted Applications (PUAs). This malware can also harvest system information and send it to remote servers managed by its operators. 

According to SentinelOne threat researcher Phil Stokes, these large-scale and continuing attacks began in early November 2020, with a spike in activity commencing in July and early August. 

AdLoad will install a Man-in-the-Middle (MiTM) web proxy after infecting a Mac to compromise search engine results and incorporate commercials into online sites for financial benefit. 

It will also acquire longevity on infected Macs by installing LaunchAgents and LaunchDaemons, as well as user cronjobs that run every two and a half hours in some circumstances. 

According to SentinelLabs, “When the user logs in, the AdLoad persistence agent will execute a binary hidden in the same user’s ~/Library/Application Support/ folder. That binary follows another deterministic pattern, whereby the child folder in Application Support is prepended with a period and a random string of digits. Within that directory is another directory called /Services/, which in turn contains a minimal application bundle having the same name as the LaunchAgent label. That barebones bundle contains an executable with the same name but without the com. prefix.” 

During the period of this campaign, the researcher witnessed over 220 samples, 150 of which were unique and went unnoticed by Apple's built-in antivirus, despite the fact that XProtect presently comprises of dozen AdLoad signatures. 

Many of the SentinelOne-detected samples are also signed with legitimate Apple-issued Developer ID certificates, while others are attested to operate under default Gatekeeper settings. 

Further, Stokes added, "At the time of writing, XProtect was last updated around June 15th. None of the samples we found are known to XProtect since they do not match any of the scanner’s current set of Adload rules." 

"The fact that hundreds of unique samples of a well-known adware variant have been circulating for at least 10 months and yet remain undetected by Apple’s built-in malware scanner demonstrates the necessity of adding further endpoint security controls to Mac devices." 

To effectively comprehend the significance of this threat, Shlayer's case can be considered which is another common macOS malware strain capable of bypassing XProtect and infecting Macs with other malicious payloads. 

Shlayer recently exploited a macOS zero-day to bypass Apple's File Quarantine, Gatekeeper, and Notarization security checks and download second-stage malicious payloads on compromised Macs. 

Even though these malware strains are just delivering adware and bundleware as secondary payloads, for the time being, their developers can, however, switch to distributing more serious malware at any point. 

Apple’s head of software, under oath, while testifying in the Epic Games vs. Apple trial in May said, "Today, we have a level of malware on the Mac that we don’t find acceptable and that is much worse than iOS."