Microsoft defeats MacSync Stealer malware by tracking behaviour, not blocking domains

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Microsoft says blocking domains is ineffective against MacSync Stealer’s evolving infrastructure

Defender experts tracked over 30 domains by analyzing behavioral patterns instead

Mitigation focuses on spotting suspicious shell sessions, osascript activity, and /tmp/sync archives

Microsoft says it has found a way to stop the dangerous MacSync Stealer malware by monitoring certain behaviors, rather than keeping track of the domains used in the attacks.

MacSync Stealer is a piece of infostealer malware built for the Apple ecosystem - it steals passwords, browser data, cookies, Keychain secrets, cryptocurrency wallets, Telegram sessions, SSH/cloud credentials and other sensitive information.

It was being distributed via ClickFix scams. Victims would visit a malicious website which would tell them they had a problem (an outdated browser or a “protected” document that can only be viewed after “verifying” identities), and which would immediately offer a solution. That solution is to bring up the Terminal and paste a command which, in reality, deployed the malware.

Initially, defenders would keep their Mac fleets safe by blocking the domains used to host the infrastructure - the websites, the malware executables, and the exfiltrated data. But they soon realized that a new domain would pop up as soon as the old one was blocked, and the malware would continue its operations unabated.

Behavioral analysis

Now, in a new report , Microsoft said it successfully identified more than 30 domains by looking at behavioral patterns such as repeated execution, request characteristics, staging behavior, and upload methods.

“Microsoft Defender Experts expanded that view by correlating recurring endpoints and network behaviors across the activity. This behavior-led approach connected more than 30 domains and showed that the infrastructure supported more than C2 communication, extending into active collection, staging, and exfiltration,” Microsoft explained.

In other words, to defend against MacSync Stealer, don’t focus on blocking domains. Instead, pay attention to shell sessions spawning ‘curl’ with specific flag combinations, osascript quickly chaining into network activity, and archives appearing under /tmp/sync just before outbound PUT traffic begins.