Office (OOXML) / .XLSX malware analysis — malicious · bbf7ec6941839f06

MALICIOUS

Office (OOXML) / .XLSX

96.9 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300

MD5: e24b4670bc9917e7612c37d540612be2 SHA-1: 9bbb7ef89c43d81f62e612830800fc7dc9e042bc SHA-256: bbf7ec6941839f06df8c1e4c817524e8259fac56ab404720259c2ed9e6dbefbb

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Service Execution: Service Execution

The file is an Excel document containing multiple Excel 4.0 macro sheets, as indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. These macro sheets are designed to execute arbitrary code upon opening. While the specific commands within the macro sheets are heavily obfuscated and truncated in the provided evidence, the presence of these macro sheets strongly suggests an attack pattern focused on initial execution and payload delivery. No specific IOCs like URLs or hashes were extracted from the macro content.

Heuristics 2

Excel 4.0 macro sheet (7 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 7

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `c37fba766abd6d156918a643e026b438f9eb0eaa225c144756cd2a5c6fda4519`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet3.bin	484 bytes
`xlm_sheet_01.bin` `22bba77ccfeebe8e5c4e883612c26774cb0b357b34f9b8f821432aab3ada7cb3`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet6.bin	484 bytes
`xlm_sheet_02.bin` `a54cfa9ba41e5598d383926a84d25941debd28f24c9934cba5a5f56d9097ca69`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2076 bytes
`xlm_sheet_03.bin` `cc1fea1c5ed0ee9ba6377487e147436c2cdc066a48105c36d0aca3c1995417f4`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet4.bin	484 bytes
`xlm_sheet_04.bin` `fc16eb2a62981f93b25a935d0a0fb49d33f90429021cb43f6e7f301424f17a92`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	484 bytes
`xlm_sheet_05.bin` `e1559372370dc0c7c16b816f71c2d5acc0e30cc8878cffe531ed647dae733bb2`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet5.bin	484 bytes
`xlm_sheet_06.bin` `1f384d37a830103e6e157bda73c1f5bba7a0a8db52a6ba5a8d8560d3886df131`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	484 bytes

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