Evading AV detection is part of a malware author's routine in crafting spam campaigns and an old and effective way of achieving this is spamming a password protected document. Recently, we observed such a password protected document being spammed out, and even worse, its payload was ransomware.
Figure 1: Email sample containing the password for the attachment "Invoice.doc"
Figure 2: User is required to input the password to open the document
The "Invoice.doc" attachment contains a macro. If the user's macro security setting is Low, the document will automatically launch the macro. Furthermore, the macro is password protected. Unfortunately, faced with this, most users will not have any idea what this document will do on the background.
Looking at the content of the macro reveals it will download a file from hxxp://209[.]141[.]59[.]124/azo.exe, then save and launch it as %temp%\qwerty2.exe. Eventually from on the same IP address, this azo.exe will download and execute hrms.exe which is the HERMES 2.1 Ransomware.
Figure 3: Macro inside the "Invoice.doc" attachment
The Hermes 2.1 Ransomware does not add its own file extension to the encrypted files. Once the infection is over, it will launch DECRYPT_INFORMATION.html from the user's desktop.
Figure 4: Hermes 2.1 Ransomware DECRYPT_INFORMATION.html
Figure 5: Enabling ActiveX will show the Ransomware Note
Interestingly, at around the same time, we also observed an email sample with same the subject and almost identical email headers and body. However, the attachment was a file called "invoice.xps", an XML Paper Specification (XPS) file. XPS was supposed to be Microsoft's answer to PDF, and Windows has a built in XPS viewer.
Figure 6: Email sample almost same as Figure 1 but with "invoice.xps" attachment and different email signatory
The attachment "invoice.xps" has FixedPage.NavigateUri property. When this is clicked, it will redirect the user to hxxp://rainbowrealty[.]com/ads/herewego.html.
Figure 7: The attachment "invoice.xps"
Figure 8: "invoice.xps" has FixedPage.NavigateUri property
Unfortunately, this URL is no longer accessible as of this writing. It could have led to the same Ransomware or other malware. What it does show is the same actors using a variety of file formats and tricks.
An email with attachment secured with a password may give some an impression of security. But, as illustrated, it pays to be cautious. The bad guys like using passwords too, mainly to try and evade gateway inspection of the attachment.
invoice.doc (38536 bytes)
azo.exe (393216 bytes)
hrms.exe (393216 bytes)
Invoice.xps (442266 bytes)