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Microsoft Uncovers Multi-Tier Supply Chain Attack

Microsoft has shared details of a new attack that attempted to spread crypto-mining malware to a large number of users by compromising the software supplying partner of an application developer.

Microsoft has shared details of a new attack that attempted to spread crypto-mining malware to a large number of users by compromising the software supplying partner of an application developer.

The multi-tier attack relied on compromising the shared infrastructure between a PDF editor vendor and one of its partners that provided additional font packages for the application: the attackers aimed at the supply chain of the supply chain.

Limited in nature, Microsoft said the compromise appeared to be active between January and March 2018, and could have impacted six other vendors working with the font package provider.

Carried out silently, the attack initially appeared as a typical infection and was automatically blocked, but the same infection pattern was observed across a large number of machines.

Windows Defender APT eventually alerted on nearly 70,000 cases incidents involving a coin mining process masquerading as pagefile.sys, which was launched by a service named xbox-service.exe, Microsoft’s Windows Defender ATP Research team explains.

Microsoft’s investigation revealed that a malicious installer package (MSI) was being downloaded by a PDF editor during installation, along with other legitimate installers. It was then discovered that the application vendor itself hadn’t been compromised, but the malicious package was served by a partner that creates and distributes additional font packages used by the app.

The attackers discovered a weakness in the interactions between the app vendor and its partner and also found a way to leverage it to hijack the installation chain of the MSI font packages, thus turning the PDF editor into the unexpected carrier of the malicious payload.

Microsoft discovered that the attackers had created a replica of the software partner’s infrastructure on their own server and copied and hosted all MSI files, including font packages, there. They only modified an Asian fonts package to add the malicious payload to it.

The attackers also managed to influence the download parameters used by the PDF app so as to point to their server, which resulted in the download of MSI font packages from the rogue server. Thus, users ended up installing the coin miner malware along with the legitimate application.

At device restart, the malicious MSI file would be replaced with the legitimate version. Microso
ft also discovered hardcoded PDF app names in the malicious package and concluded that at least six additional vendors might have been targeted by the attackers.

“While we were not able to find evidence that these other vendors distributed the malicious MSI, the attackers were clearly operating with a broader distribution plot in mind,” Microsoft says.

Detected as Trojan:Win64/CoinMiner, the malicious miner would hide behind the name xbox-service.exe and use the infected machine’s resources to mine for Monero. The malware also attempts to prevent remote cleaning and remediation by blocking communication with the update servers of certain PDF apps.

The threat also hinted at browser scripts as an alternative form of coin mining, but it’s unclear whether this was a secondary plan or work in progress.

“This new supply chain incident did not appear to involve nation-state attackers or sophisticated adversaries but appears to be instigated by petty cybercriminals trying to profit from coin mining using hijacked computing resources,” Microsoft’s says.

A CrowdStrike report published earlier this week highlighted the increasing number of cyberattacks targeting the software supply chain. Some of the largest such incidents include the NotPetya and CCleaner incidents last year, which impacted millions.

Related: Software Supply Chain Increasingly Targeted in Attacks: Survey

Related: Mitigating Risk of Supply Chain Attacks

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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