Office (OOXML) / .XLSX malware analysis — malicious · c548e534358c0729

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: e963ef875c44ecf140507a4d7fcd8472 SHA-1: 83fbf79d1327c2d42e7b52b94d35f0090ffa7f4d SHA-256: c548e534358c07290a4bebebf723d8cc96f9889d940e4082157844642bc2a82b

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an XLSX file containing an embedded Excel 4.0 macro sheet. The heuristics indicate the presence of XLM macros, which are often used to download and execute malicious payloads. The macro content is heavily obfuscated and truncated, preventing a precise determination of its actions, but the presence of XLM macros strongly suggests an intent to run arbitrary commands.

Heuristics 2

Excel 4.0 macro sheet (1 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 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `c03a19a43999132e3e943a64d9f09c145c1ff1f3e7ec64136db086ccbbd870ca`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	1811 bytes

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