Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 553d5db98c37896a…

MALICIOUS

Office (OOXML) / .XLSX

235.1 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300
MD5: 3a23eb1bab849a292579bf8f6d086f3e SHA-1: 948265ef862c1b5844bf4515cb0b86702e014b2a SHA-256: 553d5db98c37896ad952bf1b31a8247b3da11c4ec1c14bf4bd7c67efee8a8f07
180 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic

The file is identified as a malicious Excel macro-enabled spreadsheet containing Excel 4.0 macros. The ClamAV detection name 'Xls.Downloader.DarkTheme122101-9913615-0' strongly suggests its function as a downloader. The embedded XLM macrosheet, though truncated in the provided evidence, is characteristic of malware that executes arbitrary code or downloads further stages. The primary function appears to be the initial delivery of a malicious payload.

Heuristics 3

  • Excel 4.0 macro sheet (1 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.DarkTheme122101-9913615-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.DarkTheme122101-9913615-0

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
ed50b803f90e464df712b8a23061db8268c639cd565dbebdb887f5816e0dc985		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 141726 bytes

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