- Kaspersky uncovers MacSync, a Mac infostealer delivered via iCloud calendar events and fake apps
- Loader fetches instructions from calendar entries, then deploys malware exfiltrating credentials, wallets, and developer data
- Newer variants add Objective‑C backdoor spoofing Finder, persistence, and expanded targeting of crypto and IT users
Cybercriminals have found a way to use iCloud calendar events and cloud storage to deliver a powerful infostealer to Mac devices.
The malware is called MacSync, and it’s hiding behind fake crypto wallets, or “cracked” commercial software.
Security researchers Kaspersky, who discovered the ongoing campaign, are urging Mac users to exercise caution when downloading programs, especially from third-party websites, and to be very skeptical of apps prompting for their admin password.
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Why calendar?
Getting people to download and run malware on their devices is not as easy as it sounds.
The victims need to be somehow tricked into downloading and running an app, and even when they do so, chances are the malicious program will be sniffed out by whatever antivirus solutions the device has running, before it can do any meaningful damage. Also, crooks don’t want to be forced to repeat the process every time they want to deploy a different variant, or type of malware.
So, they resort to all sorts of techniques and workarounds, from DLL sideloading, to malware loaders.
By separating the initial infection and the actual malware, cybercriminals can reduce detection rate and get more flexibility, but it creates a new problem: defenders can monitor the traffic going in and out of different apps and thus detect when a loader is deploying malware.
The challenge then becomes hiding the traffic, and MacSync does it by using the iCloud calendar.
After being downloaded and executed, the loader will reach out to the calendar – which is a totally benign activity that is unlikely to raise any suspicion – and look for a specific public event, pre-built by the attackers. In its description, it will find the instructions, and the location of, the actual infostealer, and deploy it to ultimately compromise the target device. In this case, the location was also in the iCloud.
The loader itself is being advertised through social media, SEO poisoning, and phishing. Victims are directed either to fraudulent websites or social media channels promoting cracked software, or free versions of advanced solutions. In at least one example, Kaspersky saw the loader being advertised as a cryptocurrency wallet. Victims are shown a typical ClickFix error, and told to fix it by pasting a command in the Terminal.
The command deploys the loader which, in turn, installs MacSync.
A “substantial” overhaul
The infostealer emerged in April 2025, and was initially spun out of AMOS, one of the most popular information-stealing variants for the MacOS. It is based on Swift and has, since then, evolved to offer additional capabilities. According to Kaspersky, it can exfiltrate browser history, cookies, saved credentials, cryptocurrency wallet and app data, Telegram data, Keychain data, as well as system and device information. It can exfiltrate SSH, AWS, Kubernetes, Git, and shell configuration files, as well.
Newer variants come with an Objective-C backdoor spoofing the macOS default file manager, Finder. It establishes persistence, terminates notification processes to prevent alerts, and grants the attackers backdoor access, including running AppleScript received from the C2 server, deploying browser extensions, replacing the legitimate Ledger wallet app, collecting additional system information, and more.
Kaspersky also found an undefined command called “live_browser”, which downloads and runs a component named “sn_relay”, whose point has not yet been established.
The new versions “significantly” differ from older ones, Kaspersky said, stressing that the attackers “substantially” overhauled their approach.
“The nature of the data attackers seek to collect from a victim’s device, as well as the categories of applications the stealer disguises itself as, clearly indicates that this malware family primarily targets developers, crypto enthusiasts, and other users associated in some way with IT and the crypto space,” the researchers stressed. “MacSync’s compromise of software developers’ devices poses particular security risks for both end users and corporate systems, opening up expanded opportunities for attackers to further their intrusion.”
The full list of indicators of compromise (IoC) can be found on this link.
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