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Zyklon Malware Delivered via Recent Office Flaws

A piece of malware known as Zyklon has been delivered by cybercriminals using some relatively new vulnerabilities in Microsoft Office, FireEye reported on Wednesday.

A piece of malware known as Zyklon has been delivered by cybercriminals using some relatively new vulnerabilities in Microsoft Office, FireEye reported on Wednesday.

Zyklon has been around since early 2016 and it allows attackers to conduct a wide range of malicious activities, including launch distributed denial-of-service (DDoS) attacks, log keystrokes, steal passwords, and mine cryptocurrency.

A recent campaign observed by FireEye has been aimed at organizations in the telecommunications, insurance and financial services sectors. The malware has been delivered as a ZIP archive attached to spam emails.

The ZIP file contains a specially crafted Word document that exploits one of three weaknesses in Microsoft Office to deliver a PowerShell script that downloads the final Zyklon payload from a remote server.

One of the vulnerabilities exploited by the malicious documents is CVE-2017-8759, a flaw patched by Microsoft in September 2017 after FireEye noticed that it had been exploited to deliver spyware. The security hole was later used by China-linked cyberspies to target organizations in the United States.

Another flaw exploited to deliver Zyklon is CVE-2017-11882, a 17-year-old vulnerability in the Equation Editor component that Microsoft patched in November. CVE-2017-11882 has been leveraged by Iranian cyberspies, the Cobalt hacking group, and others.

Cybercriminals have also abused the Dynamic Data Exchange (DDE) feature in Office to spread the malware. Russia-linked cyberspies and many other threat actors have abused DDE to deliver malware, which ultimately led to Microsoft disabling the feature in all versions of Word in an effort to prevent attacks.

If the malicious documents successfully exploit one of these weaknesses, they download a PowerShell script that injects code and fetches the final payload from a server.

The malware uses the Tor network to communicate with its command and control (C&C) server. Once a connection has been established, the attacker can instruct the malware to provide information about the infected system, launch DDoS attacks, mine cryptocurrency, and upload harvested data.

In addition to built-in functionality, Zyklon has several plugins that can be loaded for additional features. The plugins allow attackers to steal passwords from popular web browsers, FTP and email passwords, keys associated with video games, and software license keys.

The malware can also establish a Socks5 proxy on the infected machine, and it can hijack the clipboard in order to replace Bitcoin addresses copied by the victim with addresses owned by the attacker.

Related: Microsoft Patches Zero-Day Vulnerability in Office

Related: Locky Uses DDE Attack for Distribution

Written By

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.

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