Office (OOXML) / .XLSX malware analysis — malicious · c8e92167752e3f5e

MALICIOUS

Office (OOXML) / .XLSX

94.2 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 16.0300

MD5: bd657f6b29da2cea491228152892cf5f SHA-1: fb9bb4127afb739fe7c6bc299be14f5d08d93497 SHA-256: c8e92167752e3f5e692f0045ff5fd24060434eeb597e5a898a2b8a0962db4ea4

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

The file is an XLSX document containing embedded Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. These macro sheets are designed to execute arbitrary commands. While the exact commands are obfuscated and truncated in the provided script excerpts, the presence of these macro sheets strongly suggests an intent to download and execute a secondary payload, a common technique for malware delivery. The specific macro sheet filenames are included as IOCs.

Heuristics 2

Excel 4.0 macro sheet (2 sheet(s)) critical OOXML_XLM_MACROSHEET

Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
XLSB international XLM macro sheet hidden in .xlsx critical OOXML_XLSB_INTL_MACROSHEET_IN_XLSX

OOXML package is named .xlsx but contains XLSB workbook parts and an international Excel 4.0 macro sheet. This hides XLM macro execution from scanners that trust the extension or only inspect XML worksheet parts. The technique is macro execution, not a document-parser CVE.

Extracted artifacts 2

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `3f8db13af710fc4012ee5afb18ac21606b10f6307f1ca1192d9c191e0487c25b`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	9034 bytes
`xlm_sheet_01.bin` `f697ee5ed6aa2dc2333e560eda58b21fd0a9b4315f1cc12bcc32630116f57256`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	1176 bytes

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