Office (OOXML) / .XLSX malware analysis — malicious · b8b328270f7a8d71

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 6de046c8baf2d1bbcf2a34876b4b4d5b SHA-1: 87e5906751cd29abc86a2f3e95fde43ac55d3414 SHA-256: b8b328270f7a8d71b800a386402cff6784035057fcf1229bc1a0fd633cd1fba6

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, indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. These macros are designed to execute arbitrary code, likely for downloading and running a second-stage payload. The obfuscated nature of the macro content prevents a more detailed analysis of the specific actions taken.

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` `c3fd41e1553dbc0c85c6191c8880ca8e5ea2fb8b84b0a25910813a334ab55ec8`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet3.bin	428 bytes
`xlm_sheet_01.bin` `a924b15e477bf4d1a47b51e022ca0c2d2a7b02c1716e7777fe19bfbcf13342ae`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet6.bin	428 bytes
`xlm_sheet_02.bin` `fa2d0734b961bfe0111204b4a4d82ccb36b2d523a20a1258847828d87611cb2a`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet4.bin	428 bytes
`xlm_sheet_03.bin` `0b00fddc0f1a841eb1156267de044fc4c3fcdc2084038541b5a578f42cc54cdd`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	1995 bytes
`xlm_sheet_04.bin` `3f22ecd3b92065ef2e650eb963ec44372ab8b477a7069f8b48cc1aa0b1233b17`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	428 bytes
`xlm_sheet_05.bin` `de48f28ca9c031e534ca9bb26e4d6627ca78f55297e89122f6c4c40ac55f5e49`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet5.bin	428 bytes
`xlm_sheet_06.bin` `7b3fec6d8a07cb1fc45180af2906e58d6d68ade2ab663c2d72d1bbfeb1cad197`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	428 bytes

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