Office (OOXML) / .XLSX malware analysis — malicious · b79c9b08f8a01e10

MALICIOUS

Office (OOXML) / .XLSX

1.16 MB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-29

MD5: 3a9dceb5ddf6679ebaae360a08be4396 SHA-1: 23b45b4f9f385550d07b4f8c860ffc5300a6ad11 SHA-256: b79c9b08f8a01e10b930bd7775a2b185049a910255ec0ebf437cea3fce4c2909

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an XLSX file containing multiple Excel 4.0 macro sheets. These macro sheets are heavily obfuscated but indicate the use of macro functionality to execute commands. The presence of these macro sheets is a strong indicator of malicious intent, likely to download and execute a secondary payload. No specific family could be identified due to the obfuscation and lack of clear indicators.

Heuristics 2

Excel 4.0 macro sheet (3 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 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`emf_00.emf` `a12daa770fc1848e39c880d90376e8e5b6814576e9bdbfaa076685fd9b9b2ba3`	ooxml-emf	OOXML EMF part: xl/media/image1.emf	6145428 bytes
`xlm_sheet_00.bin` `94dcae400bad291e7734b3303be72f72bc74b4ef3f7737fe960644bb383a7a69`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	484 bytes
`xlm_sheet_01.bin` `6b69a539d2d44586cd29d86a91c29f1e2ba8aa4a323b5a4a9f7f0d23cd002d42`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	484 bytes
`xlm_sheet_02.bin` `46ff111a4683eea3ae97021320d38aa4eb315350d26452c986cde8fd19a80a92`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2165 bytes

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