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

Static analysis result for SHA-256 e7762fab3e17b255…

MALICIOUS

Office (OOXML) / .XLSX

235.1 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300
MD5: 194cab026dad2c034f79777352fd20ff SHA-1: 583116cf98ac62122496755443dfd20b594e09bb SHA-256: e7762fab3e17b25542d5d40d6f0b52e6f86c9f99aa04317ca8673f43302fbe58
180 Risk Score

Malware Insights

MITRE ATT&CK
T1566.002 Spearphishing with Other Weapons T1059.005 Visual Basic T1204.002 Malicious File

The file is identified as a malicious Excel macro-enabled spreadsheet by ClamAV, specifically as 'Xls.Downloader.DarkTheme122101-9913615-0'. The presence of an Excel 4.0 macro sheet within the XLSX file indicates it is designed to execute code upon opening. While the macro content is truncated, the heuristic firings strongly suggest it functions as a downloader, likely executing a second-stage payload. The primary IOC is the ClamAV detection name, which often includes family or campaign information.

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
0cb80ae7f2cabcc1831e5f255ca97ce73b8c4f1ef3bf47cf48b4ce53ccce41f6		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 141726 bytes

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