Office (OOXML) / .XLSX malware analysis — malicious · 8e7acc152682d46a

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 2c0766574777d9defafa4df8bd0fd9b4 SHA-1: c7981bedac7e22fd5f3acd4f24faf04ee0d0b968 SHA-256: 8e7acc152682d46a2305e2f2aa2ae19b1871e85dd4ee19e3de5d773822648ff9

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

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. One of the macro sheets contains a truncated string that appears to be a call to 'URLDownloadToFile', suggesting the macro's purpose is to download a second-stage payload from a remote location. The exact URL and final payload could not be determined due to truncation.

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` `fe8c9bbdebbc101416d357c0f8b1467b3ffc665d3ad3b6464d779efc546018fe`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	363 bytes
`xlm_sheet_01.bin` `142c474f5b65f41f7487d7bd4b30317f3f15749f7bb00ef30c374ff4e8d3b8b5`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	363 bytes
`xlm_sheet_02.bin` `fb8f9f78c965d57c77f790338149ee0188b49113617e3bb658be0b6bcc69820c`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	3349 bytes
`xlm_sheet_03.bin` `7b50d126e61d11c7426b0f6d0b36768dce1391a8a85e3d336d13dbb55080b769`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet3.bin	363 bytes
`xlm_sheet_04.bin` `9b5f9daf898ff1888f9647c1f8eff3f98bca443912da43ad7e9f2c19e06204ca`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet4.bin	363 bytes
`xlm_sheet_05.bin` `8f084010ac0788038b52a75bc18f911a978b28ffba13c420a026f47a896abc25`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet5.bin	2589 bytes
`xlm_sheet_06.bin` `a38f77b14843d06a8b906b2c62d403b9f55d6e3d60dabd356ab0a67117713c28`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet6.bin	2023 bytes

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