Office (OOXML) / .XLSX malware analysis — malicious · 36f1e0d29978e7d3

MALICIOUS

Office (OOXML) / .XLSX

142.9 KB Created: 2015-06-05 18:17:20 UTC Authoring application: Microsoft Excel 16.0300

MD5: 3203909dafc1211d9f6c6dc71d231d81 SHA-1: d7ae83187f8ddf5f53ad2dd32da187707af0eaf5 SHA-256: 36f1e0d29978e7d38365c91e23c65647b2fb7aa74f56d341777a25108ba6658c

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications

The file is an XLSX document containing multiple embedded Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. While the specific commands within the truncated macro sheets are not fully discernible, the presence and nature of these macros strongly suggest an intent to execute arbitrary code. This is a common technique for downloading and executing further stages of malware. No specific family could be identified due to the obfuscated and truncated nature of the macro content.

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 3

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `d32efc890f8d678c4f7f726763ce14626df10566923007b6e4657be22c95a744`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	6043 bytes
`xlm_sheet_01.bin` `8c6ef244f1b5655417d57f29f2b866c60f538fb6fe24b0d818f3382f72b7314f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	1210 bytes
`xlm_sheet_02.bin` `bef0998d7885927ea99b5d89ac0fb6c92b8b3ec6a42066e003a1824f1de3b019`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet3.bin	5857 bytes

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