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

Static analysis result for SHA-256 8fb50871b4f3ac66…

MALICIOUS

Office (OOXML) / .XLSX

62.9 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 3c23d893b981dd2de016b9b59c2de311 SHA-1: cfd2f0841a69ff297488ff804c87c44f38480768 SHA-256: 8fb50871b4f3ac66944a7370c53b7418556e65a7890bf380a39aa2380e83573b
60 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic for Applications

The sample is an Excel file containing Excel 4.0 macros. The macros appear to be attempting to write a file to disk at 'C:\ProgramData\fnsfunSfgRgnKjFsgNd'. This is indicative of a downloader or initial access stage, likely intended to fetch and execute a further payload. The exact execution mechanism is not fully discernible due to truncation, but the intent is clear.

Heuristics 1

  • 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.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
7167f58fe8c913e8b3f4c4e3cebce8d5d0688127b9eecccd0ae4391fe9fe0422		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 4080 bytes

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