Threat actors leverage old email conversation threads to spread Emotet

• Threat actors revive old email conversation threads to inject a link to an Emotet-infected file.
• The tactic has been previously used by a North Korean hacker group to target various individuals.

The operators of Emotet trojan have evolved their tactics to spread the malware. Lately, they have been observed reviving old email conversation threads to inject a link to an Emotet-infected file.

How does it work - Users involved in the previous email exchanges would receive an email that pretends to be from the previous correspondents. However, the email actually comes from Emotet servers.

The email conversation thread would be left intact but the Emotet gang would insert an URL at the top of the email that would link to an Emotet-infected file or a malicious document.

How old is the tactic - The tactic has been previously used by a North Korean-based hacking group to target various individuals across the world. In 2017, Palo Alto Networks Unit 42 researchers had noted that the threat actors had leveraged the tactic to compromise multiple email accounts tied to a legitimate domain in North East Asia.

How long the Emotet gang is using the tactic - The Emotet gang has taken this new approach in October last year. This enabled the group to launch a mass-harvesting campaign.

According to a report from Cofense, the gang has been actively using the tactic from April 9, 2019, thus calling it as a ‘Major evolution in the way Emotet works’.

This new Emotet email thread spam isn’t limited to English emails. The operators are also leveraging English and German email threads to launch attacks.

"The injected reply is usually prefaced with 'Attached is your confidential docs. These templates are pretty limited in run and not very numerous compared to the 'normal' [Emotet] malspam," said Cryptolaemus Group researcher Joseph Roosen, ZDNet reported.

Which other malware has used the tactic - The creators of URSnif trojan used a similar tactic in March and October 2018. They created the email threads from scratch, instead of reviving the threads, to spread the malware.