Office (OOXML) / .XLSX malware analysis — malicious · 20de13d2ac1e2676

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 9e158f9f5850de1d2ee9949973b18867 SHA-1: 4f566bc7bd2752acfb3853a220178c227daf080d SHA-256: 20de13d2ac1e26769986fdee712bcb7c531469798bd776083c7fde5058a7796b

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications T1105 Ingress Tool Transfer

The sample contains multiple Excel 4.0 macro sheets, as indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The macro content explicitly reconstructs URLs and uses them to download files named 'Tot1.docx', 'Tot2.docx', and 'Tot3.docx'. The macro also calls 'regsvr32.exe' with these downloaded files, suggesting an attempt to execute malicious content or further stages of an attack. The ClamAV detection further confirms its malicious nature as a downloader.

Heuristics 3

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.
ClamAV: Xls.Downloader.Docusign112101-9908076-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Xls.Downloader.Docusign112101-9908076-0

Extracted artifacts 3

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `18ede813231036332942d996e36a6488e975dcc53afe6d4dcc84bcbb3bee9f13`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	363 bytes
`xlm_sheet_01.bin` `515f997acf460ac8917a480f954ef565ab8102df1eb6c65521ded110938edf9f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	2518 bytes
`xlm_sheet_02.bin` `57b1134ff2d46209ab069c79a03ae4bf9258a7c9574d5e080d9850650f633264`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	1038 bytes

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