Office (OOXML) / .XLSX malware analysis — malicious · 94d388ab5646b340

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 00b49f7204d19971880a9a2629b4f7ce SHA-1: 45f6176d073e6f0394f7f293479f8f15c2222687 SHA-256: 94d388ab5646b3400aa45894ef0ff7e084894e25e3b3286f92ca630c613ea10c

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications 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. The extracted macro content includes a function named 'URLDownloadToFileTo', suggesting the macro's purpose is to download a second-stage payload from a URL. The specific URL is not fully extracted due to truncation, but the function name itself is a strong indicator of malicious intent.

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` `27470e6f36371ac46933a280c5142a0e60c649006ea912d00ad5061bc4a7ea27`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	363 bytes
`xlm_sheet_01.bin` `24c338fcb5dcdc07a0439014ff58ab74bdcb595185c6089e659c4434d267ed6a`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	3373 bytes
`xlm_sheet_02.bin` `46a50827ae31cc1d5489437e7f78847a8e9e1786bc4dc927f5099e4f714c83d0`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	3339 bytes

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