North Korea Hackers Using New "Dolphin" Backdoor to Spy on South Korean Targets

The North Korea-linked ScarCruft group has been attributed to a previously undocumented backdoor called Dolphin that the threat actor has used against targets located in its southern counterpart.

"The backdoor [...] has a wide range of spying capabilities, including monitoring drives and portable devices and exfiltrating files of interest, keylogging and taking screenshots, and stealing credentials from browsers," ESET researcher Filip Jurčacko said in a new report published today.

Dolphin is said to be selectively deployed, with the malware using cloud services like Google Drive for data exfiltration as well as command-and-control.

The Slovak cybersecurity company said it found the implant deployed as a final-stage payload as part of a watering hole attack in early 2021 directed against a South Korean digital newspaper.

The campaign, first uncovered by Kaspersky and Volexity last year, entailed the weaponization of two Internet Explorer flaws (CVE-2020-1380 and CVE-2021-26411) to drop a backdoor named BLUELIGHT.

ScarCruft, also called APT37, InkySquid, Reaper, and Ricochet Chollima, is a geo-political motivated APT group that has a track record of attacking government entities, diplomats, and news organizations associated with North Korean affairs. It's been known to be active since at least 2012.

Earlier this April, cybersecurity firm Stairwell disclosed details of a spear-phishing attack targeting journalists covering the country with the ultimate goal of deploying a malware dubbed GOLDBACKDOOR that shares overlaps with another ScarCruft backdoor named BLUELIGHT.

The latest findings from ESET shed light on a second, more sophisticated backdoor delivered to a small pool of victims via BLUELIGHT, indicative of a highly-targeted espionage operation.

This, in turn, is achieved by executing an installer shellcode that activates a loader comprising a Python and shellcode component, the latter of which runs another shellcode loader to drop the backdoor.

"While the BLUELIGHT backdoor performs basic reconnaissance and evaluation of the compromised machine after exploitation, Dolphin is more sophisticated and manually deployed only against selected victims," Jurčacko explained.

What makes Dolphin a lot more potent than BLUELIGHT is its ability to search removable devices and exfiltrate files of interest, such as media, documents, emails, and certificates.

The backdoor, since its original discovery in April 2021, is said to have undergone three successive iterations that come with its own set of feature improvements and grant it more detection evasion capabilities.

"Dolphin is another addition to ScarCruft's extensive arsenal of backdoors abusing cloud storage services," Jurčacko said. "One unusual capability found in prior versions of the backdoor is the ability to modify the settings of victims' Google and Gmail accounts to lower their security, presumably in order to maintain account access for the threat actors."

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