Nuclear Submarine Designer

A threat actor believed to be working on behalf of Chinese state-sponsored interests was recently observed targeting a Russia-based defense contractor involved in designing nuclear submarines for the naval arm of the Russian Armed Forces.

The phishing attack, which singled out a general director working at the Rubin Design Bureau, leveraged the infamous "Royal Road" Rich Text Format (RTF) weaponizer to deliver a previously undocumented Windows backdoor dubbed "PortDoor," according to Cybereason's Nocturnus threat intelligence team.

"Portdoor has multiple functionalities, including the ability to do reconnaissance, target profiling, delivery of additional payloads, privilege escalation, process manipulation static detection antivirus evasion, one-byte XOR encryption, AES-encrypted data exfiltration and more," the researchers said in a write-up on Friday.


Rubin Design Bureau is a submarine design center located in Saint Petersburg, accounting for the design of over 85% of submarines in the Soviet and Russian Navy since its origins in 1901, including several generations of strategic missile cruiser submarines.

Nuclear Submarine Designer
Content of the weaponized RTF document

Over the years, Royal Road has earned its place as a tool of choice among an array of Chinese threat actors such as Goblin Panda, Rancor Group, TA428, Tick, and Tonto Team. Known for exploiting multiple flaws in Microsoft's Equation Editor (CVE-2017-11882, CVE-2018-0798, and CVE-2018-0802) as far back as late 2018, the attacks take the form of targeted spear-phishing campaigns that utilize malicious RTF documents to deliver custom malware to unsuspecting high-value targets.

This newly discovered attack is no different, with the adversary using a spear-phishing email addressed to the submarine design firm as an initial infection vector. While previous versions of Royal Road were found to drop encoded payloads by the name of "8.t," the email comes embedded with a malware-laced document, which, when opened, delivers an encoded file called "e.o" to fetch the PortDoor implant, implying a new variant of the weaponizer in use.


Said to be engineered with obfuscation and persistence in mind, PortDoor runs the backdoor gamut with a wide range of features that allow it to profile the victim machine, escalate privileges, download and execute arbitrary payloads received from an attacker-controlled server, and export the results back to the server.

"The infection vector, social engineering style, use of RoyalRoad against similar targets, and other similarities between the newly discovered backdoor sample and other known Chinese APT malware all bear the hallmarks of a threat actor operating on behalf of Chinese state-sponsored interests," the researchers said.

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