Patchwork Cyberspies Adopt New Exploit Techniques
12.12.2017 securityweek CyberSpy
Malware campaigns attributed to the Patchwork cyberespionage group have been using a new delivery mechanism and exploiting recently patched vulnerabilities, Trend Micro warns.

Also known as Dropping Elephant or Chinastrats and believed to be operating out of the Indian subcontinent, the group is said to have been active since 2014. Initially focused on government-associated organizations that have connections to Southeast Asia and the South China Sea, the actor has expanded its target list to include entities in a broad range of industries.

In a new report (PDF) on Patchwork’s latest operations, Trend Micro says that the group has added businesses to its list of targets and that its use of numerous infection vectors and payloads makes it a credible threat.

Campaigns that security researchers have associated with the group over the course of 2017 revealed diverse methods (social engineering hooks, attack chains, and backdoors), along with the adoption of Dynamic Data Exchange (DDE), Windows Script Component (SCT), and exploits for recently reported vulnerabilities.

“These imply they’re at least keeping an eye on other threats and security flaws that they can repurpose for their own ends. Also of note are its attempts to be more cautious and efficient in their operations,” Trend Micro notes.

Targets and attack vectors

The observed campaigns focused on multiple sectors in China and South Asia, but also hit organizations in the U.K., Turkey, and Israel. Using spear-phishing emails, the cyberespionage group targeted high-profile personalities, business-to-consumer (B2C) online retailers, telecommunications and media companies, aerospace researchers, and financial institutions. The United Nations Development Programme was targeted as well.

The spear-phishing emails contained website redirects, direct links, or malicious attachments. Some emails contained direct links to malicious documents hosted on the attacker-owned servers. The group spoofed a news site and used it to divert visitors to socially engineered, malware-ridden documents and was also observed misusing email and newsletter distribution services.

A fake Youku Tudou website (a social video platform popular in China) was used for drive-by downloads. The victim was tricked into downloading and executing a fake Adobe Flash Player update that was, in fact, a variant of the xRAT Trojan.

Patchwork was also observed phishing for credentials to take over a target’s emails and other online accounts. One attack copied a webpage from a legitimate web development company and displayed the fake page to victims alone.

Using Rich Text Format (RTF) documents, the group exploited vulnerabilities such as CVE-2012-1856 – a remote code execution (RCE) in the Windows common control MSCOMCTL, or CVE-2015-1641 – a memory corruption in Microsoft Office. They also exploited the CVE-2014-4114 Sandworm RCE vulnerability in Windows’ Object Linking and Embedding (OLE) via PowerPoint (PPSX) files.

More recent vulnerabilities the actor has been abusing include CVE-2017-0199 – an RCE in Microsoft Office’s Windows OLE, patched in April 2017, and CVE-2017-8570 – an RCE in Microsoft Office patched in July 2017. They were exploited via PowerPoint (PPT) and PPSX files.

The malicious PPSX files exploiting CVE-2017-8570 downloaded a Windows Script Component (SCT) file from a Patchwork-owned server to eventually deliver the xRAT malware.

“Apart from exploit-laden documents, Patchwork also misused DDE to retrieve and execute xRAT in the infected machine. They also sent a document embedded with an executable, which downloads a decoy document and a backdoor, then executes the latter,” Trend Micro explains.

Malware and infrastructure

In addition to using a variety of malicious documents for their nefarious purposes, the Patchwork hackers also deployed a miscellany of backdoors and information stealers onto their victims’ machines. Some of these tools appear to be used solely by this group, the security researchers say.

The threat actor was observed dropping malware such as the NDiskMonitor custom backdoor (believed to be Patchwork’s own, it can list files and logical drives and download and execute files from specified URLs); and Socksbot, which can start Socket Secure (SOCKS) proxy, take screenshots, and run executables and PowerShell scripts.

Malware such as the xRAT remote access tool (its source code is available online) and the Badnews backdoor (potent information-stealing and file-executing malware) were also associated with the group’s activities, as well as a series of file stealers (Taskhost Stealer and Wintel Stealer targeting .doc, .docx, .xls, .xlsx, .ppt, .pptx, .pdf, and RTF files, along with .eml and .msg email messages; as well as versions of file stealers written in AutoIt).

Trend Micro has discovered 30 to 40 IP addresses and domain names used by the group in 2017 and says that each of the servers has had a different purpose. While some were only meant as command and control (C&C) servers that would collect data from the used stealers, others were used only to host phishing websites.

In some cases, the same server was being used for both C&C communication and to host distributing malware (or malicious documents) through hosting content copied from legitimate websites.

The group has been using publicly available PHP scripts for retrieving files from the server without disclosing their real paths, likely to prevent security researchers from finding open directories. Trend Micro also observed the group temporarily removing a file so it could not be retrieved or replacing it with a legitimate one. Sometimes they would display “a fake 302 redirection page to trick researchers into thinking the files are gone.”

“Patchwork is in a vicious cycle, given the group’s habit of rehashing tools and malware. The more those are used, the likelier that they’d be incorporated in the group’s arsenal. The takeaway for enterprises? The gamut of tools and techniques at Patchwork’s disposal highlights the significance of defense in depth: arraying proactive defense to thwart threats at each level—from the gateways, endpoints, and networks to servers,” Trend Micro notes.