Office (OLE) / .XLSX malware analysis — malicious · d4b29d6e46f83eaf

MALICIOUS

Office (OLE) / .XLSX

82.0 KB Created: 2020-05-20 08:20:55 Authoring application: Microsoft Excel

MD5: c62c026e48e72a658d81eead7117716c SHA-1: 3b236b076d753379d8c6d38a24273618c4a67b0a SHA-256: d4b29d6e46f83eafa20ec05a42b0690367507976968dbdebbeabcd8f76ba39d0

140 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

The critical heuristics OLE_XLM_AUTOOPEN and OLE_XLM_DANGEROUS_FN indicate the presence of Excel 4.0 macros with Auto_Open functionality, specifically utilizing the RUN function (439). The document body contains a partially obfuscated URL, 'http://os.mediarncbx.com/DGvqBLj', which is likely used to download and execute a second-stage payload. The use of XLM macros suggests an older, but still effective, delivery mechanism.

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` `9e43f94b2c3cf18dbd12eae2dc81db7a7694aa2af38505c6fc337c80c4fbc45c`	xlm-macro	oletools.olevba.extract_all_macros (XLM macro listing)	48494 bytes

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