Threat actors utilizing the Snake keylogger malware for Windows are emailing malicious PDFs with embedded Word documents to breach its victims’ PCs and steal private data. 

According to threat analysts at HP’s Wolf Security who earlier detected the PDF malware campaign, malicious PDFs are an unusual tool to use currently as attackers normally opt to use Office formats like Word and Excel as these are more familiar to PC users. 

The malicious PDFs infect PCs with Snake, a keylogger and credential stealer initially detected in late November 2020. 

The threat actors sent email with an attached PDF document named “REMMITANCE INVOICE.pdf” which includes an embedded Word document named “has been verified. 

However PDF, Jpeg, xlsx, .docs’ may contain programs, macros, or viruses that are harmful for the infected computer.

Should the user opt to “Open the file”, Microsoft Word opens. As HP mentions, if Protected View is disabled, Word downloads a Rich Text Format (.rtf) file from a web server, which is then run to open the document. 

HP’s analysts discovered an illegitimate URL from which an external object linking and embedding (OLE) object was loaded. The OLE object also has shellcode that exploits the CVE-2017-11882, an old remote code execution vulnerability in Microsoft Office Equation Editor that is still being exploited by attackers to this day. 

The exploited vulnerability in this campaign (CVE-2017-11882) is over four years old, yet continues being used, suggesting the exploit remains effective for attackers,” HP says.