LinkedIn Phishing Ramps Up With More-Targeted Attacks

Phishing attacks are targeting out-of-work users on LinkedIn, creating lures using job titles scraped from the targeted workers' profiles in an attempt to convince them to open and execute different malicious files or links, according to a new analysis from cybersecurity firm eSentire.

The attack involves a tool known as "more_eggs" — a fileless backdoor program that consists of a script that runs in memory and calls various system functions to compromise the target's computer. The latest variant of the scheme uses a malicious ZIP archive labeled with the target's title from LinkedIn and then uses a LNK file to execute.

The attack shows the degree to which attackers — in this case, a group dubbed "Golden Chickens" — are improving personalization and targeting to increase the likelihood of their success, says Rob McLeod, senior director of the Threat Response Unit (TRU) for eSentire.

"The personalization and the effort that this group has gone to in order to make a convincing lure is significant," he says. "A lot of the tradecraft is not new, and we have seen this tradecraft used by other groups before, but at this point, it shows the extent that threat actors are willing to go to create a believable lure."

The attack targeted a professional in the healthcare technology industry, according to eSentire's analysis.

The attack is not new, with security firm Proofpoint describing similar attacks in 2019 using an older version of the "more_eggs" backdoor. The attackers used a fake profile created on LinkedIn to contact potential targets and then followed up in e-mail, sending a variety of malicious attachments or links. Sometimes, the attackers would wait as much as a week before following up.

"As threat actors continue to turn away from very large-scale 'spray and pray' campaigns and focus on persistent infections with downloaders, RATs [remote access Trojans], bankers, and other malware, increasingly sophisticated social engineering and stealthy malware are making their way into a range of campaigns," Proofpoint states in its analysis. "This actor provides compelling examples of these new approaches, using LinkedIn scraping, multi-vector and multistep contacts with recipients, personalized lures, and varied attack techniques to distribute the More_eggs downloader, which in turn can distribute the malware of their choice based on system profiles transmitted to the threat actor."

The current campaign is likely performing an access-for-hire service, where the threat actor compromises systems and then either sells access or installs malware of the criminal client's choice. In the past, "more_eggs" has been connected to the financial cybercrime group FIN6, another financial threat group known as Evilnum, and the Cobalt Group, according to eSentire.

The use of the "more_eggs" script underscores the increase usage of fileless malware by attack groups. Such living-off-the-land techniques have become very popular because they make detection more difficult. In a report published last week, security firm WatchGuard found that its detections of fileless malware increased by a factor of 8 in the past year.

The attack also underscores the difficulty for any single layer of security to detect and block such attacks. The company may not own the endpoint and also cannot protect its employees' personal accounts. The social media network may not be able to determine what information and identities are fraudulent without an unacceptable level of monitoring. And the users do not always have the level of technical aptitude needed to spot scams. 

The solution is to use all three approaches, says McLeod. "We have to have user awareness training, so [defense] doesn't depend on the platform that you are executing on — verify who you are speaking to and don't trust attachments," he says. "Social media companies will play a part because they need to make fake information and fraudulent profiles ... completely obvious. And finally, the company also has a responsibility to protect their endpoints."