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

Static analysis result for SHA-256 1207ee0d6671c37b…

MALICIOUS

Office (OOXML) / .XLSX

114.4 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300
MD5: 3b1830655e7189332c97880d4391694a SHA-1: 1e506d9b231ed61506af3f68c7b81ac31d61d8db SHA-256: 1207ee0d6671c37bc66f9636d2f61105832c487b8a87edccce2de9ba4d569471
180 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

The file contains Excel 4.0 macros, identified by multiple critical heuristics. These macros are designed to reassemble and execute a command-line payload. Specifically, the reassembled command is 'regsvr32 -s', which is typically used to download and execute a second-stage payload from a remote source, indicating a downloader or droppper functionality.

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.
  • Excel 4.0 macro sheet stored under disguised package path critical OOXML_XLM_DISGUISED_RELATIONSHIP
    OOXML package declares an xlMacrosheet relationship whose target is outside the canonical xl/macrosheets/ path. Excel follows the relationship type, while path-only scanners can miss the macro execution surface.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
3fd2c5ac9f1339b006d4b8558a66e92632e93690860205c61803635b864cb6a6		 xlm-macrosheet OOXML XLM macro sheet: xl/xls/sheet1.bin 1007414 bytes

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