Microsoft Threat Intelligence identified a new strain of XCSSET, a complex modular macOS malware that targets Xcode programs. The malware was discovered in the wild during routine threat hunting, and it is the first known XCSSET variant to appear since 2022.
This latest version of XCSSET includes improved obfuscation methods, updated tactics for maintaining persistence on infected workstations, and new ways to infect systems. These enhancements enable the malware to steal and exfiltrate files, as well as sensitive system and user information, such as digital wallet data and private notes.
XCSSET is meant to infect Xcode projects and runs when a developer builds them. Since Xcode is frequently used by Apple and macOS developers, Microsoft believes the malware spreads by exploiting shared project files amongst developers. While this edition has some similarities with previous versions, it features a more modular structure and encoded payloads.
Harder to detect and eliminate
In order to evade detection by security, it also has improved error handling and makes extensive use of scripting languages, UNIX commands, and genuine system binaries. It can sometimes even function without leaving files on disc, which makes them more challenging to locate and delete. To make it harder for analysts to comprehend its operations, the malware conceals the names of its modules at the code level.
Additionally, it employs more sophisticated obfuscation techniques, like randomly generating and encoding payloads when infecting Xcode projects. The most recent version of XCSSET also employs Base64 for encoding, in contrast to previous versions that solely used xxd (hexdump).
To ensure that it continues to run, the malware exploits three separate persistence methods: it runs when a new shell session is started, when a user opens a fake Launchpad program, or when a user makes a Git commit. It also includes a new method for injecting malware payloads directly into targeted Xcode projects.
Microsoft's analysis also revealed that some of the malware appears to be still in development. Its command-and-control (C2) server was operational at the time Microsoft released its report, and it was releasing new modules. Microsoft recommends developers and security teams to remain careful and keep an eye on their Xcode projects and environments for any unusual activity.
Surge in macOS assaults
The latest ransomware is just one example of the sophisticated attacks that have increased against macOS systems, according to Thomas Richards, Principal Consultant, Network and Red Team Practice Director at Black Duck.
“The techniques seen in this malware show that the developers spent a considerable amount of time researching ways to remain undetected. Gone are the days where macOS users could operate without installing anti-virus or EDR software. To prevent these attacks from spreading, users of Xcode should make sure their endpoint protection software is up to date and run scans to determine if they’ve been infected or not,” Richards stated.
Threat to Apple developers
With its improved ability to conceal within Xcode projects and propagate when these projects are shared between teams, this new XCSSET variant poses a serious threat to Apple developers, stated J Stephen Kowski, Field CTO at SlashNext.
“This sophisticated attack targets the software supply chain at its source, potentially compromising apps before they’re even built, with the malware’s improved obfuscation techniques and multiple persistence methods making it particularly difficult to detect. Real-time code scanning and advanced threat detection tools that can identify suspicious behaviors in development environments are essential for protecting against these types of attacks,” Kowski noted.
He recommends developers to use multi-layered security measures, such as constant monitoring of project files for unexpected changes and rigorous verification of all code sources prior to integration.