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

Static analysis result for SHA-256 9e05cd392d9c1334…

MALICIOUS

Office (OOXML) / .XLSX

427.5 KB Created: 2015-06-05 18:17:20 UTC Authoring application: Microsoft Excel 16.0300
MD5: b53ed71b3c7a18f70d693a137b5adc5c SHA-1: a31f1a98ea227e331303ec0c6ee226a711427998 SHA-256: 9e05cd392d9c1334c404ceb8fe28d6bc179d9844569bced9d2d1c057de538dee
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic

The file is an XLSX document containing multiple embedded Excel 4.0 macro sheets. These macros are known to be capable of executing arbitrary code. While the specific commands within the macros are heavily obfuscated and truncated in the provided evidence, the presence of these macro sheets strongly suggests an intent to download and execute a second-stage payload. No specific family could be identified due to the obfuscation.

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
5c37caf3972147003d306c83c7cc3ea0779d1361ef8a2e025b110a5d83d88326
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 1195 bytes
xlm_sheet_01.bin
647ca0f9ba7c0d89747dcd9cda74b5117564c642c828c186a0583317683e5bf0
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin 1235 bytes
xlm_sheet_02.bin
d337facfc0bb951495bfb4bb88cc36b9c8979e5f04405de89fabb113738d03a0
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet3.bin 2027 bytes