Security Experts:

XCSSET Mac Malware Steals Information, Spreads via Xcode Projects

A newly discovered piece of malware designed to target macOS systems spreads through Xcode projects and exploits what researchers have described as two zero-day vulnerabilities.

Named XCSSET, the malware can allow its operator to steal sensitive information and launch ransomware attacks, Trend Micro reported on Thursday. Specifically, it can help hackers obtain information associated with the Evernote, Skype, Notes, QQ, WeChat, and Telegram apps, capture screenshots, and upload files to the attackers’ server.

It can also encrypt files and display a ransom note, and it can launch universal cross-site scripting (UXSS) attacks in an effort to inject JavaScript code into the websites visited by the victim. This allows it to modify websites, including replacing cryptocurrency addresses, and steal credentials for online services and payment card information from the Apple Store.

One aspect that makes XCSSET interesting is the fact that it spreads via projects for Xcode, Apple’s integrated development environment for macOS. The attackers inject malicious code into Xcode projects and the code gets executed when the project is built.

Trend Micro says it has spotted two Xcode projects injected with the malware, one on July 13 and one on July 31. While these particular projects are less likely to be integrated by other developers into their own projects, the cybersecurity company warns that the distribution method can be highly effective if more popular projects are compromised, leading to what it described as a “supply-chain-like attack.”

“We have also identified this threat in sources such as VirusTotal, which indicates this threat is at large,” Trend Micro warned.

It also noted, “Affected developers will unwittingly distribute the malicious trojan to their users in the form of the compromised Xcode projects, and methods to verify the distributed file (such as checking hashes) would not help as the developers would be unaware that they are distributing malicious files.”

An analysis of the C&C server used by XCSSET revealed a list of 380 victim IP addresses, including 152 in China and 103 in India. However, Trend Micro says it has nothing to share at this time regarding a possible connection to known threat actors.

The company’s researchers also discovered that XCSSET exploits what appear to be two zero-day vulnerabilities. One is related to Data Vaults, which are designed to protect against unauthorized access to data whether or not the requesting app is itself sandboxed. The malware exploits this vulnerability to steal a Safari cookie file, which stores information associated with visited websites. Trend Micro noted that exploitation of this vulnerability requires either another sandbox escape flaw or admin privileges on the targeted system.

The second apparent zero-day vulnerability exploited by XCSSET enables the attackers to run the development version of Safari when the victim opens the web browser. The development version is not sandboxed, allowing the attacker to inject malicious JavaScript code that can run without restrictions. The malicious code is injected via a UXSS attack.

Trend Micro told SecurityWeek that it reported its findings to Apple, and while the company is working on making changes in future versions of macOS that could mitigate the Data Vault-related flaw, Apple sees the issue related to the development version of Safari as intended behavior.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.