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

Static analysis result for SHA-256 024032a776ffcc3c…

MALICIOUS

Office (OOXML) / .XLSX

117.2 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300
MD5: f72f128268c37a4a69c27dbc7ca06232 SHA-1: 0f4ea1a9e66746c2afd00e82d9c47e0a9331736d SHA-256: 024032a776ffcc3cc6753aa47bd1198e98209c04a8c606d80feb5108e97a6bef
180 Risk Score

Malware Insights

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

The file contains disguised Excel 4.0 macros, identified by critical heuristics. These macros reassemble a command string that uses 'wmic process call create' to execute 'regsvr32 -s', indicating an attempt to download and run a second-stage payload. The specific command suggests a downloader or dropper 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
2006239d8bb47d136ec03377b55c75ca7192ce4ee9c173461133f96e6641a4e7		 xlm-macrosheet OOXML XLM macro sheet: xl/uie/sheet1.bin 1130224 bytes

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