Attackers Already Targeting Apple's M1 Chip with Custom Malware

The latest processor for Apple's Macs — the M1 chip — has already become a target for malware authors, who have created Mac-specific binaries targeting the ARM64 architecture used by the processors, researchers said this week.

For example, one MacOS malware downloader, dubbed Silver Sparrow, has a number of interesting properties, including the use of the MacOS installer's JavaScript API to create persistence, and communication with a command-and-control (C2) infrastructure built on Amazon Web Services (AWS) servers and Akamai's content distribution network (CDN), security firm Red Canary stated in an analysis of the new malware. In addition, the malware also natively runs on the latest Macs running the M1 ARM64 architecture.

While creating a native binary for the ARM64 architecture is an interesting step on the part of attackers, the development merely allows the malware to run a bit faster and may avoid some x86-focused security measures, says Tony Lambert, intelligence analyst at Red Canary.

"This threat didn't take advantage of any particular feature unique to M1 itself," he says, but adds that "the malware has a greater chance of success on M1 systems due to the [relative lack of] availability of security tools for the new architecture."

Attackers have traditionally focused on Mac systems as an afterthought, since Windows-based computers have historically dominated business applications. However, that has changed over the past decade, with nation-state attackers and more sophisticated hackers focusing on Mac systems, and cybercriminals attempting to focus on legal gray areas, such as adware. In 2020, for example, almost all malware encountered by Mac users was adware or potentially unwanted programs (PUPs), not malware.

In the case of Silver Sparrow, the creation of an M1-specific binary is merely a point of interest, says Lambert. The malware platform does not currently have any subsequent stage, so its hourly attempts to contact the operator's C2 infrastructure does not result in the installation of additional features or functions, according to Red Canary.

Yet, while tailoring the code to the M1 chip requires little effort on the part of the malware authors — just compiling the code on an M1 Mac will do — the fact that someone has done so indicates that attackers are looking to the future. In addition, security firms could be behind the curve, says Lambert.

"Since the architecture changed, software developers need to recompile their products and test for the new systems," he says. "As a result, some security vendors haven't fully caught up to the technology change."

Non-native ARM64 programs use an Apple technology known as Rosetta to run on M1-based Macs. Because the malware does not have to go through the Rosetta system for backward compatibility, it could avoid detection.

Independent researcher Patrick Wardle searched the malware repository VirusTotal for information on recent binaries and found at least one program that appears to be a malicious M1 executable. Malicious M1 programs appear to evade detection by current antivirus systems, he stated in an analysis.

"[M]ore worrisomely, [static] analysis tools or anti-virus engines may struggle with ARM64 binaries," he wrote. "Unfortunately detections of the arm64 version dropped roughly 15%—when compared to the standalone x86_64 version—[and] several industry leading AV engines, who readily detected the x86_64 version, failed to flag the malicious ARM64 binary."

Another anti-detection approach: The Silver Sparrow malware also uses the JavaScript API to automate installation and persistence, something researchers have not seen in Mac malware in the past and that security software might miss, Red Canary's Lambert says.

"If defenders have detection analytics written to look for malicious pre-install or post-install scripts — one usual route taken by malicious installers — using the JavaScript API to invoke commands will evade those detection analytics because it produces a different pattern in telemetry," Lambert says. "In this case, using JavaScript causes the legitimate macOS installer process to invoke the commands without indicating the precise source within the installer package."

Red Canary and other security firms notified Apple and Amazon of the issues, and both companies have taken steps to blunt the impact of Silver Sparrow. Apple has revoked the specific developer IDs used to create the malware, and Amazon has worked to prevent access to the specific S3 buckets used by the malware infrastructure. 

"Thankfully, that risk is decreasing due to the response of Apple and Amazon ... they both have internal processes to investigate and remove malicious use of their systems," Lambert says. "That said, it's still possible that versions of Silver Sparrow exist in the wild that no vendors have observed and that use different S3 instances or callback domains. Those users would definitely be at risk."

While a non-M1 version of the C2 infrastructure appeared in mid-August, the malware infrastructure was updated in December with the M1 download domains in December. The actual programs have both been submitted to VirusTotal in the last month.