Security researchers discovered that a threat actor is targeting LinkedIn users with fake job offers to deliver the More_eggs backdoor.

Since mid-2018, Proofpoint has observed various campaigns distributing More_eggs, each of which began with a threat actor creating a fraudulent LinkedIn profile. The attacker used these accounts to contact targeted employees at U.S. companies — primarily in retail, entertainment, pharmaceuticals and other industries that commonly employ online payments — with a fake job offer via LinkedIn messaging.

A week after sending these messages, the attacker contacted the targeted employees directly using their work email to remind them of their LinkedIn correspondence. This threat actor incorporated the targets’ professional titles into subject lines and sometimes asked recipients to click on a link to a job description. Other times, the message contained a fake PDF with embedded links.

These URLs all pointed to a landing page that spoofed a legitimate talent and staffing management company. There, the target received a prompt to download a Microsoft Word document that downloaded the More_eggs backdoor once macros were enabled. Written in JScript, this backdoor malware is capable of downloading additional payloads and profiling infected machines.

A Series of Malicious Activities on LinkedIn

The threat actor responsible for these campaigns appears to have had a busy 2019 so far. Proofpoint found ties between these operations and a campaign first disclosed by Krebs on Security in which phishers targeted anti-money laundering officers at U.S. credit unions. Specifically, the security firm observed similar PDF email attachments and URLs all hosted on the same domain.

This isn’t the first time an online actor has used LinkedIn for malicious activity, either. Back in September 2017, Malwarebytes Labs found evidence of attackers compromising peoples’ LinkedIn accounts and using them to distribute phishing links via private messages. Less than a year later, Alex Hartman of Network Solutions, Inc. disclosed a similar campaign in which threat actors attempted to spread malware via LinkedIn using fake business propositions.

How to Defend Against Backdoors Like More_eggs

Security professionals can help defend against backdoors like More_eggs by consistently monitoring endpoints and devices for suspicious activity. Security teams should simultaneously use real-time compliance rules to automate remediation in the event they observe behavior that appears to be malicious.

Additionally, experts recommend testing the organization’s phishing defenses by contacting a reputable penetration testing service that employs the same tactics, techniques and procedures (TTPs) as digital criminals.