Office (OLE) / .XLSX malware analysis — malicious · 133decfab02d9316

MALICIOUS

Office (OLE) / .XLSX

36.0 KB Created: 2020-11-27 11:38:34 Authoring application: Microsoft Excel

MD5: 203aa46caea486d7578659d69a45ee01 SHA-1: be1d9eb9cf84a67cf9767fc0a705b6af4aed52b6 SHA-256: 133decfab02d9316407c78c916e10dae8979bd6234eca3a67069dea6bfea118f

140 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1203 Exploitation for Client Execution

The file contains Excel 4.0 macros, specifically an Auto_Open defined name, which is a critical finding indicating automatic execution upon opening. The heuristic also flags the use of dangerous formula APIs, including RUN, suggesting the macro is designed to execute external commands. This points to a downloader or dropper functionality, where the macro likely initiates the download and execution of a secondary malicious payload.

Heuristics 3

Excel 4.0 Auto_Open defined name critical OLE_XLM_AUTOOPEN_DEFINEDNAME

oletools recovered an Auto_Open / Auto_Close entry from an Excel 4.0 macro sheet. The raw BIFF name can be tokenized or partially opaque to byte-string checks, but the recovered macro listing confirms the workbook has an XLM auto-execution entry.
XLM Auto_Open with dangerous formula APIs critical OLE_XLM_DANGEROUS_FN

Excel 4.0 macro sheet contains an Auto_Open / Auto_Close entry and dangerous XLM formula APIs that can invoke programs, write files, or transfer control without VBA.
Excel 4.0 (XLM) macro sheet present medium OLE_XLM_AUTOOPEN

Workbook contains an Excel 4.0 macro sheet sub-stream — XLM is rarely seen in modern legitimate workbooks and was a major Office malware vector during 2020-2022.

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_macros.txt` `243fc2e1ab8c0b29c786871b5828a626355c1da41214075ba0820b2e0ae64ee6`	xlm-macro	oletools.olevba.extract_all_macros (XLM macro listing)	6520 bytes

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