Ransomware developers have leveraged the EternalBlue exploit, now the criminals behind the Retefe banking Trojan have added the NSA exploit to their arsenal.

The EternalBlue exploit was released in April by the hacking group Shadow Brokers and was used in the global WannaCry ransomware attacks. The exploit was also used, along with other attack vectors, to deliver the NotPetya wiper and more recently, has been incorporated into the TrickBot banking Trojan.

The Retefe banking Trojan is distributed via malicious Microsoft Office documents sent via spam email. In order for the Trojan to be installed, the emails and the attachments must be opened and code must be run. The attackers typically use Office documents with embedded objects which run malicious PowerShell code if clicked. Macros have also been used in some campaigns to deliver the malicious payload.

Researchers at Proofpoint have now obtained a sample of the Retefe banking Trojan that includes the EternalBlue SMBv1 exploit. The EternalBlue module downloads a PowerShell script and an executable. The script runs the executable, which installs the Trojan.

The researchers noted the module used in the WannaCry attacks that allowed rapid propagation within networks – Pseb – was lacking in Retefe, although that may be added at a later date. It would appear that the criminals behind the campaign are just starting to experiment with EternalBlue.

Other banking Trojans such as Zeus have been used in widespread attacks, although so far attacks using the Retefe banking Trojan have largely been confined to a limited number of countries – Austria, Sweden, Switzerland, Japan, and the United Kingdom.

Businesses in these countries will be vulnerable to Retefe, although due to the number of malware variants that are now using EternalBlue, all businesses should ensure they mitigate the threat. Other malware variants will almost certainly be upgraded to include EternalBlue.

Mitigating the threat from EternalBlue (CVE-2017-0144) includes applying the MS17-010 patch and also blocking traffic associated with the threat through your IDS system and firewall. Even if systems have been patched, a scan for vulnerable systems should still be conducted to ensure no devices have been missed.

Since the Retefe Trojan is primarily being spread via spam email, a spam filter should be implemented to prevent malicious messages from reaching end users. By implementing SpamTitan, businesses can protect their networks against this and other malware threats delivered via spam email.