On Friday, the U.S. Department of Homeland Security’s (DHS) computer emergency readiness team (US-CERT) issued a new warning about phishing attacks on energy companies and other critical infrastructure sectors.

Advanced persistent threat (APT) actors are conducting widespread attacks on organizations in the energy, aviation, nuclear, water, and critical manufacturing sectors. Those attacks, some of which have been successful, have been occurring with increasing frequency since at least May 2017. The group behind the attack has been called Dragonfly by AV firm Symantec, which reported on the attacks in September.

DHS believes the Dragonfly group is a nation-state sponsored hacking group whose intentions are espionage, open source reconnaissance and cyberattacks designed to disrupt energy systems.

These cyberattacks are not opportunistic like most phishing campaigns. They are targeted attacks on specific firms within the critical infrastructure sectors. While some firms have been attacked directly, in many cases the attacks occur through a ‘staging’ company that has previously been compromised. These staging companies are trusted vendors of the targeted organization. By conducting attacks through those companies, the probability of an attack on the target firm succeeding is increased.

DHS warns that the attackers are using several methods to install malware and obtain login credentials. The phishing attacks on energy companies have included spear phishing emails designed to get end users to reveal their login credentials and malicious attachments that install malware.

In the case of the former, emails direct users to malicious websites where they are required to enter in their credentials to confirm their identity and view content. While some websites have been created by the attackers, watering hole attacks are also occurring on legitimate websites that have been compromised with malicious code. DHS warns that approximately half of the attacks have occurred through sites used by trade publications and informational websites “related to process control, ICS, or critical infrastructure.”

Phishing emails containing malicious attachments are used to directly install malware or the files contain hyperlinks that direct the user to websites where a drive-by malware download occurs. The links are often shortened URLS creating using the bit.ly and tinyurl URL shortening services. The attackers are also using email attachments to leverage Windows functions such as Server Message Block (SMB) protocol to retrieve malicious files. A similar SMB technique is also used to harvest login credentials.

The malicious attachments are often PDF files which claim to be policy documents, invitations, or resumés. Some of the phishing attacks on energy companies have used a PDF file attachment with the name “AGREEMENT & Confidential.” In this case, the PDF file does not include any malicious code, only a hyperlink to a website where the user is prompted to download the malicious payload.

US-CERT has advised companies in the targeted sectors that the attacks are ongoing, and action should be taken to minimize risk. Those actions include implementing standard defenses to prevent web and email-based phishing attacks such as spam filtering solutions and web filters.

Since it is possible that systems may have already been breached, firms should be regularly checking for signs of an intrusion, such as event and application logs, file deletions, file changes, and the creation of new user accounts.