Threat actors are delivering the Zyklon Malware exploiting three Office vulnerabilities

Security experts from FireEye have spotted a new strain of the Zyklon malware that has been delivered by using new vulnerabilities in Microsoft Office.

Researchers at FireEye reported the malware was used in attacks against organizations in the telecommunications, financial, and insurance sectors.

Zyklon has been spotted for the first time in 2016, it is a publicly available malware that could be used for multiple purposes such as espionage campaigns, DDoS attacks or to mine cryptocurrency.

“FireEye researchers recently observed threat actors leveraging relatively new vulnerabilities in Microsoft Office to spread Zyklon HTTP malware.” reads the analysis published by FireEye.

“Zyklon is a publicly available, full-featured backdoor capable of keylogging, password harvesting, downloading and executing additional plugins, conducting distributed denial-of-service (DDoS) attacks, and self-updating and self-removal.”

The malware is modular, it can download several plugins to implement different features, it may communicate with C&C server over The Onion Router (Tor) network.

In this last campaign, the malicious code has been delivered via spam emails using as a ZIP archive that contains a specially crafted Word document.

The document exploits one of three vulnerabilities in Microsoft Office to deliver a PowerShell script that downloads the final Zyklon payload from a remote server.

One of the flaws exploited by the attackers is CVE-2017-8759, a flaw that was fixed by Microsoft in September 2017 after it was exploited by threat actors such as the Cobalt group to deliver malware in attacks wild.

A second triggered by the documents used in the campaign spotted by FireEye is CVE-2017-11882, a 17-year-old vulnerability in MS Office that could be exploited by remote attackers to install a malware without user interaction.
The flaw is a memory-corruption issue that affects all versions of Microsoft Office released in the past 17 years, including the latest Microsoft Office 365. The vulnerability could be triggered on all versions of Windows operating system, including the latest Microsoft Windows 10 Creators Update.

The vulnerability affects the MS Office component EQNEDT32.EXE that is responsible for insertion and editing of equations (OLE objects) in documents.

This flaw was used by differed APT groups, including the Cobalt group and Iran-linked hackers.

The attackers also exploited the Dynamic Data Exchange (DDE) feature in Office to deliver the malicious code, the same feature was abused by at least one Russian APT group in cyber espionage campaigns and by the powerful Necurs botnet to deliver ransomware.

Once the malware has successfully exploited one of these flaws, it will download a PowerShell script that injects code and fetches the final payload from a remote server.

FireEye highlighted the fact that attackers are exploiting recently discovered flaws in widely adopted software such as the Office suite to increase the likelihood of infecting the victims’ machines.

“Threat actors incorporating recently discovered vulnerabilities in popular software – Microsoft Office, in this case – only increases the potential for successful infections. These types of threats show why it is very important to ensure that all software is fully updated. Additionally, all industries should be on alert, as it is highly likely that the threat actors will eventually move outside the scope of their current targeting.” concludes FireEye.

Technical details about the threat, including the Indicators of Compromise, are available in the report published by FireEye.

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Pierluigi Paganini

(Security Affairs –Zyklon malware, Office)

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