North Korea-linked Zinc group posed as Samsung recruiters to target security firms

North Korea-linked threat actors posed as Samsung recruiters in a spear-phishing campaign aimed at employees at South Korean security firms.

North Korea-linked APT group posed as Samsung recruiters is a spear-phishing campaign that targeted South Korean security companies that sell anti-malware solutions, Google TAG researchers reported.

According to the Google Threat Horizons report, the state-sponsored hackers sent fake job offers to employees at the security companies. Google TAG researchers reported that the same group, tracked as Zinc,” also targeted security researchers in past campaigns

“TAG observed a North Korean government-backed attacker group that previously targeted security researchers posing as recruiters at Samsung and sending fake job opportunities to employees at multiple South Korean information security companies that sell anti-malware solutions.” reads the Google Threat Horizons report. “The emails included a PDF allegedly claiming to be of a job description for a role at Samsung; however, the PDFs were malformed and did not open in a standard PDF reader. When targets replied that they could not open the job description, attackers responded with a malicious link to malware purporting to be a “Secure PDF Reader” stored in Google Drive which has now been blocked.”

The attackers used a malformed PDF claiming to be a job description for a role at Samsung, for this reason, the recipient was not able to open it and contacted the sender that in turn provided him with a link to a “Secure PDF Reader” app.

The app, which was stored in Google Drive, was a tainted version of the legitimate PDF reader PDFTron. Upon installing the app a backdoor is established on the victims’ devices.

The activity of the Zinc APT group, aka Lazarus, surged in 2014 and 2015, its members used mostly custom-tailored malware in their attacks. This threat actor has been active since at least 2009, possibly as early as 2007, and it was involved in both cyber espionage campaigns and sabotage activities aimed to destroy data and disrupt systems.

The group is considered responsible for the massive WannaCry ransomware attack, a string of SWIFT attacks in 2016, and the Sony Pictures hack. The attackers targeted the researchers through multiple social networking platforms, including Twitter, LinkedIn, Telegram, Discord, and Keybase.

Threat actors used a network of fake profiles to get in contact with researchers of interest. In mid-2020, ZINC hackers created Twitter profiles for fake security researchers that were used to retweet security content and posting about vulnerability research. 

Attackers used Twitter profiles for sharing links to a blog under their control (br0vvnn[.]io), to share videos of their claimed exploits, and for amplifying and retweeting posts from other accounts under their control.

Once established initial communications, the attackers would ask the targeted security researcher if they wanted to collaborate on vulnerability research together, and then shared with it a Visual Studio Project.

The Visual Studio project used by the attackers included the source code for exploiting the vulnerability along with an additional DLL that would be executed through Visual Studio Build Events, which is a backdoor.

The Visual Studio project was containing a malicious DLL that would be executed when researchers compiled the project.

The malicious code would lead to the installation of a backdoor that would allow the attackers to take over the target’s computer.

The attackers published a blog post titled “DOS2RCE: A New Technique To Exploit V8 NULL Pointer Dereference Bug” and shared it via Twitter. The researchers who visited the post from October 19 to 21, 2020, using the Chrome browser, were infected with a known ZINC malware. Microsoft researchers noticed that some of the victims were using fully patched browsers, a circumstance that suggests that attackers used 0-day exploits. Not all visitors to the site were infected.

Attackers also used other techniques to target security professionals, for example in some cases distributed blog posts as MHTML files that contained some obfuscated JavaScript that was pointing to a ZINC-controlled domain for further JavaScript to execute. 

In one case, attackers attempted to exploit, without success, the CVE-2017-16238 vulnerability in a vulnerable driver for the antivirus product called Vir.IT eXplorer.

The recent attacks against South Korean anti-malware suggest the interests of threat actors in compromising the supply chain of South Korean security organizations in order to target their customers.

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Pierluigi Paganini

(SecurityAffairs – hacking, North Korea)

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