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

Static analysis result for SHA-256 141a23ce14ba6702…

MALICIOUS

Office (OOXML) / .XLSX

97.1 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: 9a33b86fa2ee2372023d418129238b25 SHA-1: d94101917d187df6bd710f2abf288cf9f2ee86c9 SHA-256: 141a23ce14ba6702fdba9d074fe66eab9f9084be7030033b0258656942a3c660
180 Risk Score

Malware Insights

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

The file contains Excel 4.0 macros that are designed to download and execute secondary payloads. Specifically, the macros construct URLs pointing to .ocx files in the ProgramData directory and then use 'regsvr32' to execute them. This indicates a downloader functionality.

Heuristics 3

  • 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.
  • 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.
  • ClamAV: Xls.Downloader.Docusign112101-9908076-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Docusign112101-9908076-0

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
30e7f1eb7b7cda9226667aa44630e34cb4e61815c9b73ffde1c06f2d016d24d9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 363 bytes
xlm_sheet_01.bin
924c95acbe52d08cb50364609116239c27cf91b6440c18d7744972648a370d60		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 2900 bytes
xlm_sheet_02.bin
e80c1b37f3c5cec1142f106d8141d8a69bae7bc3fbf9a747d153a562b95978ef		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin 1676 bytes

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