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

Static analysis result for SHA-256 b7e2110f58b55841…

MALICIOUS

Office (OOXML) / .XLSX

472.7 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: 48e940d2e1a709ad3c6672d7a09c2993 SHA-1: 46d123c22d3ad668fb7309cdfe2fb715bd8fdf9f SHA-256: b7e2110f58b55841828c604815da9539cd24465b1f66e4bed82b5b33370229e3
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The sample is an XLSX file containing embedded Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The macro content includes calls to 'URLDownloadToFile', indicating an intent to download and execute a second-stage payload. The specific URL is not fully reconstructed due to truncation, but the technique is clear.

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.

FilenameKindSourceSize
xlm_sheet_00.bin
e93b62ceabff5670c6b070b22e93b6dd88ba1d8d6bb1b2470c57d8e6e5e4afcc
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 363 bytes
xlm_sheet_01.bin
8f8c08b94b8c1687c5806e2e790af5cbb3c642ca4f5d49972f31a898fc59ebfd
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 3037 bytes
xlm_sheet_02.bin
c1430d30e9e9353fa9c8255370417ac19fa117f3de74c55cc3cbe80e2b7ea8c4
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin 3079 bytes