New PamStealer macOS Malware Uses Clever Tradecraft To Remain Stealthy

An anonymous reader quotes a report from Ars Technica: 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. [...] PamStealer shows a native password prompt designed to resemble a system authorization request. Text that appears with the prompt says: "Maccy wants to make changes. Enter your password to allow this." As noted earlier, once a target complies, the malware validates it locally through the PAM API. "This check is done entirely through PAM: there is no call out to dscl, security, osascript or any spawned process to verify the password, as many commodity macOS stealers do," [said Jamf, a security firm for macOS users]. "The result is a quieter routine that keeps only a verified password, and one fewer process chain for defenders to detect on." If the validation fails, PamStealer displays the prompts again until it receives the correct one. Once the target enters the correct password, PamStealer displays a message stating that the file is damaged and can't be installed. This is designed to be a decoy to prevent the target from suspecting anything is amiss. The malware uses tactics to maximize the information it can steal. One tactic is to request the target grant full disk access to the fake Maccy app. It also contains code designed to access ethereum accounts. The various techniques -- particularly the Script Editor lure, a self-contained JXA dropper, a Rust-based second stage, and local validation of credentials through PAM are all noteworthy.

Read more of this story at Slashdot.