The concept of file-less malware is not a new one. Families like Poweliks, which abuse Microsoft’s PowerShell, have emerged in recent years and have garnered extensive attention due to their ability to compromise a system while leaving little or no trace of their presence to traditional forensic techniques.
System administrators have lauded the power and versatility of PowerShell since version 2.0’s integration into Windows 7. Unfortunately, with such versatility comes the opportunity for abuse, specifically surrounding the capability to write directly into memory of the host OS.
Typically, file-less malware has been observed in the context of Exploit Kits such as Angler. Palo Alto Networks has observed a recent high-threat spam campaign that is serving malicious macro documents used to execute PowerShell scripts which injects malware similar to the Ursnif family directly into memory. We call the malware PowerSniff.
First, victims are presented with an email similar to the image below:
At the time of writing, Palo Alto Networks has observed roughly 1500 emails sent using a variety of filenames. The majority of these emails contain specific information about the victim’s company, such as their phone number, physical address, as well as the name of the individual. This additional information is not typically included in widespread spam campaigns, and can often provide a sense of trust when seen by the victim, which in turn may lead to a higher number of opened attachments.
In the event a victim opens the malicious Microsoft Word document attached within the email, they will be subjected to a malicious macro contained within this file. The following example macro attempts to execute when the document initially opens. Depending on the security settings of Microsoft Word, victims may need to explicitly enable the macro to run.
This widespread spam campaign has been witnessed in the past week. Due to the target-specific details contained within the spam emails and the use of memory-resident malware, this particular campaign should be treated as a high threat. As this malware relies on malicious macros within Microsoft Word documents, users should ensure that macros are not enabled by default and should be wary of opening any macros in files received from untrusted sources.
Palo Alto Networks WildFire customers are protected against this threat, as all encountered files have been correctly flagged as malicious. Additionally, all C2 domains currently encountered have also been marked malicious. AutoFocus users can identify this malware using the PowerSniff tag.
The researchers would like to thank Cert.pl’s @maciekkotowicz for his excellent analysis of the configuration data of the malware.