A recent campaign is pushing 2 RATs, encrypted, packed, and hidden in PNG files – using disk image files again and redirectors as arrival vectors.
The first spam campaign is about fake harassment. The sender, claiming to be a school president, is informing his colleague that an anonymous email with video, supposedly in the attachment, shows sexual harassment occurred on their premises.
The attachment CONFIDENTIAL0056.zip is a ZIP archive. Inside it is a disk image file CONFIDENTIAL0056.iso which is the Universal Disk Format (UDF) file system format. The image file CONFIDENTIAL0056.iso contains a RAR self-extracting archive (RARSfx) file PRIORITY.scr. Once launched, the RARSfx will silently drop and install 3 files in the %temp% folder. First, a shortcut file Xnekm.lnk will be created. It points to and therefore runs an executable Zhknjdc.exe which is in a folder with the same name as the LNK file. Stored with the EXE file is an image file Zhkn.png.
A related spam campaign was spotted using fake purchase emails. The attachment PO-1109017834665.xlsx.html, disguised as an order slip, is an HTML redirector. It contains a META refresh tag that leads to the download of a RAR file. The HTML also has a hidden paragraph tag with random word padding causing the huge file size of the attachment.
The downloaded file PO-1109017834665.xlsx.rar is a RAR archive which contains 1 file PO-1109017834665.xlsx.exe – a Delphi compiled executable. The EXE’s behavior is almost the same with the EXE file dropped by RARSfx from the first campaign, except the associated PNG is located at its overlay, in other words appended to the end of the executable.