The Sednit threat group recently added a Delphi dropper and mail downloader to its Zebrocy tool set of downloaders, droppers and backdoors.

Researchers from ESET detected a new phishing campaign distributing the malware. The operation begins with a Delphi dropper that, once activated, loads and executes an Ultimate Packer for Executables (UPX)-packed Microsoft Intermediate Language (MSIL) downloader. This downloader gathers more than a dozen pieces of information and sends them to the attackers via email to retrieve a Delphi mail downloader.

A new addition to Zebrocy distribution campaigns, the Delphi mail downloader enables Sednit to assess the importance of an infected machine. The attackers then proceed with the campaign using the Delphi mail downloader to exfiltrate data and retrieve commands from the operator via emails and passwords. The mail downloader ultimately drops a Delphi downloader, which is responsible for executing the final Delphi backdoor payload.

Zebrocy: A Brief History

According to ESET, Sednit has been distributing the Zebrocy malware since at least 2016. In those operations, the family consisted largely of three components: a Delphi downloader, an AutoIt downloader and a Delphi backdoor. In some cases, the threat group omitted the Delphi downloader entirely.

Sednit’s decision to start a campaign with a dropper and use a Delphi mail downloader marks a new stage of delivery for its toolset; so does its decision to use the same weaponized documents for distributing multiple payloads. Palo Alto Networks witnessed this firsthand when it observed a campaign distributing Zebrocy and Cannon, a new first-stage payload that uses email as its command-and-control (C&C) communication channel.

How to Defend Against Threat Groups Like Sednit

Security professionals can help defend their organizations against phishing attacks by taking a layered approach to email security that involves mail scanning, perimeter protection and antispam measures. They should also invest in awareness training for all employees.

Sources: ESET, ESET(1), Palo Alto Networks