Office (OOXML) / .XLSX malware analysis — malicious · 20b31f3343d80565

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: c31beb9f44aad727a9696178cb8b1a58 SHA-1: 38d05e3d1b05baaf85721061640283263b3917df SHA-256: 20b31f3343d8056522a54e84e187c6e8502ab5b46cd663a610bc786ab21f9d59

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications

The file is identified as malicious by ClamAV with the signature Xls.Downloader.GreenOffice01223-9937701-0. Static analysis revealed the presence of multiple Excel 4.0 macro sheets within the XLSX file. These macros are indicative of a downloader, likely intended to fetch and execute a secondary payload. The exact download URL or execution commands could not be definitively reconstructed due to the obfuscated nature of the macro content.

Heuristics 3

Excel 4.0 macro sheet (8 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.
ClamAV: Xls.Downloader.GreenOffice01223-9937701-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Xls.Downloader.GreenOffice01223-9937701-0

Extracted artifacts 8

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `601e373374d41fdd36dd907ce4e8dc0dc0e62d3cf33bbc6cf8c27500b3b2183f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet3.bin	428 bytes
`xlm_sheet_01.bin` `789c86435dced37b9809e0d14afad4ae4bec773ba94488e1a402ea2607098acf`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet7.bin	428 bytes
`xlm_sheet_02.bin` `75546976956b41175dda83afb5dd2f36972a4c8ee8479a35e3c993561a13e40f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2080 bytes
`xlm_sheet_03.bin` `fa2cdb3f36be3e136711bb0f17877a81a3075c3aa1f9577263203e20e17563b6`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet4.bin	428 bytes
`xlm_sheet_04.bin` `3a4f7457134bada0037c22b38f7a80bf2ab71f1bea3b2529ecec0ec1f8c4a567`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	428 bytes
`xlm_sheet_05.bin` `9503a7e1b54a411a5384744a0235d0aa88ebdfcc1d955d8bb046efd02166e80e`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet6.bin	428 bytes
`xlm_sheet_06.bin` `d467663aa96d2dc4437dcdc2fe587f90ebd44488e841fa9404c0820dcc29eda3`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	428 bytes
`xlm_sheet_07.bin` `81cd2db898416c2ec8e340d66f358552cf450627a515990768e25ebfeee99983`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet5.bin	428 bytes

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