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Researchers have found a never-before-seen piece of macOS malware that combines a series of clever tradecraft to infect Macs with stealthy, custom-developed credential-stealing code.
The malware is delivered in two stages. The first is distributed in a disk image that masquerades as Maccy, a clipboard manager for Macs. It’s compiled as AppleScript that is notable for the way it delivers the second stage. The malware is named PamStealer because the Rust-written infostealer uses the Pluggable Authentication Modules interface built into macOS to validate the target’s login password before sending it to an attacker-controlled server.
The use of both disk image and AppleScript is common in malware for Macs. More unusual is the way PamStealer combines them to gain stealth. When the AppleScript is double-clicked, it’s opened in the macOS Script Editor, where the malicious functionality is buried deep within the file.
“Rather than relying on shell commands such as curl or zsh, the AppleScript executes a self-contained JavaScript for Automation (JXA) downloader that retrieves and stages the payload using native Objective-C APIs,” researchers from Jamf, a security firm for macOS users, wrote. “Combined with a Rust-based second stage and a password capture workflow that validates credentials locally through PAM, the result is a quieter execution chain than we typically observe in commodity macOS stealers.”
When a user, expecting to install a trustworthy clipboard manager, encounters the disk image, they’re prompted to press Command-R immediately after double-clicking it. This command executes malicious code inside the AppleScript directly. It also allows the execution to bypass com.apple.quarantine, a macOS attribute that provides warnings and restrictions when executable files have been downloaded from the Internet.
arstechnica.com
The malware is delivered in two stages. The first is distributed in a disk image that masquerades as Maccy, a clipboard manager for Macs. It’s compiled as AppleScript that is notable for the way it delivers the second stage. The malware is named PamStealer because the Rust-written infostealer uses the Pluggable Authentication Modules interface built into macOS to validate the target’s login password before sending it to an attacker-controlled server.
The use of both disk image and AppleScript is common in malware for Macs. More unusual is the way PamStealer combines them to gain stealth. When the AppleScript is double-clicked, it’s opened in the macOS Script Editor, where the malicious functionality is buried deep within the file.
“Rather than relying on shell commands such as curl or zsh, the AppleScript executes a self-contained JavaScript for Automation (JXA) downloader that retrieves and stages the payload using native Objective-C APIs,” researchers from Jamf, a security firm for macOS users, wrote. “Combined with a Rust-based second stage and a password capture workflow that validates credentials locally through PAM, the result is a quieter execution chain than we typically observe in commodity macOS stealers.”
When a user, expecting to install a trustworthy clipboard manager, encounters the disk image, they’re prompted to press Command-R immediately after double-clicking it. This command executes malicious code inside the AppleScript directly. It also allows the execution to bypass com.apple.quarantine, a macOS attribute that provides warnings and restrictions when executable files have been downloaded from the Internet.
Newly discovered PamStealer isn't your typical macOS malware
The discovery underscores the increased effort being poured into Mac infostealers.
arstechnica.com
