Recently attacks launched by the China-linked threat actor APT10 against the Japanese media sector revealed the use of updated tactics, techniques and procedures (TTPs), FireEye says. 

Also known as menuPass and Stone Panda, which FireEye has been tracking since 2009, the group has a history of targeting Japanese entities. Last year, the group targeted entities in at least fourteen countries, including the website of a prominent U.S. trade association.

As part of the new attacks, spear-phishing emails carrying malicious Word documents that attempt to deliver the UPPERCUT backdoor. Known in the security community as ANEL, the malware was apparently in pre-release form (beta or release candidate) until recently, FireEye’s security researchers say. 

The documents carry a malicious VBA macro and use Japanese titles related to maritime, diplomatic, and North Korean issues (but have unreadable contents). The documents were password protected, with the password provided in the email body. 

Recent UPPERCUT samples have the timestamps overwritten and filled with zeroes and the security researchers do not have visibility into the UPPERCUT 5.2.x series, but say that minor versions might have been released every few months between December 2017 and May 2018.

The latest version also features randomized exported function names and was observed sending an error code in the Cookie header when failing to receive the HTTP response from the command and control (C&C) server. For each C&C address, the malware now has uniquely hard-coded keys it uses for encryption. 

Furthermore, in the generated network traffic, the encoded proxy information has been added in the URL query values during the C&C communication, FireEye said. 

The commands supported in the new version include: download and validate file; upload file to the C&C; load PE file; download, validate, execute file, and send output to C&C server; format the current timestamp; capture the desktop screenshot in PNG format and send it to C&C; execute received buffer via cmd.exe and send the output to the server. 

“While APT10 consistently targets the same geolocation and industry, the malware they use is actively evolving. In the newer versions of UPPERCUT, there is a significant change in the way backdoor initializes the Blowfish encryption key, which makes it harder for analysts to detect and decrypt the backdoor’s network communications. This shows that APT10 is very capable of maintaining and updating their malware,” FireEye concludes. 

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