Security experts at Trend Micro have discovered a new macOS backdoor that they linked to the APT 32 (OceanLotus, APT-C-00, SeaLotus, and Cobalt Kitty) cyber espionage group.

The APT32 group has been active since at least 2013, according to the experts it is a state-sponsored hacking group. The hackers hit organizations across multiple industries and have also targeted foreign governments, dissidents, and journalists.

Since at least 2014, experts at FireEye have observed APT32 targeting foreign corporations with an interest in Vietnam’s manufacturing, consumer products, and hospitality sectors. The APT32 is also targeting peripheral network security and technology infrastructure corporations, and security firms that may have connections with foreign investors.

The APT32 group uses custom-built malware for its attacks, the newly discovered macOS backdoor was tracked by experts at Trend Micro as OSX_OCEANLOTUS.D.

The researchers found the backdoor on macOS systems that have the Perl programming language installed.

“We identified a MacOS backdoor (detected by Trend Micro as OSX_OCEANLOTUS.D) that we believe is the latest version of a threat used by OceanLotus (a.k.a. APT 32, APT-C-00, SeaLotus, and Cobalt Kitty).” reads the analysis published by Trend Micro.

“The attackers behind OSX_OCEANLOTUS.D target MacOS computers which have the Perl programming language installed.”

The hackers used spear-phishing messages as attack vectors, the backdoor is distributed via weaponized documents attached to emails. The bait document masquerades as the registration form for an event with HDMC, an organization in Vietnam that advertises national independence and democracy.

The malicious document contains an obfuscated macros with a Perl payload. The macro extracts an XML file (theme0.xml) from the document, it is a Mach-O 32-bit executable with a 0xFEEDFACE signature that acts as a dropper for the final OSX_OCEANLOTUS.D backdoor.

“All strings within the dropper, as well as the backdoor, are encrypted using a hardcoded RSA256 key. There are two forms of encrypted strings: an RSA256-encrypted string, and custom base64-encoded and RSA256-encrypted string.” continues the report.

“Using the setStartup() method, the dropper first checks if it is running as a root or not. Based on that, the GET_PROCESSPATH and GET_PROCESSNAME methods will decrypt the hardcoded path and filename where the backdoor should be installed.”

Once the dropper has installed the backdoor, it will set its attributes to “hidden” and set file date and time to random values using the touch command:

touch –t YYMMDDMM “/path/filename” > /dev/null.

It also changes the permissions to 0x1ed = 755, which is equal to u=rwx,go=rx.

The backdoor loops on two main functions, infoClient and runHandle; infoClient is used to collect platform information and send them to the command and control (C&C) server, meanwhile runHandle implements backdoor capabilities.

The discovery of a new backdoor linked to the APT32 group confirms that the state-sponsored crew was very active in the last months.

Pierluigi Paganini

(Security Affairs – APT 32, state-sponsored hacking)

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