Office (OOXML) / .XLSX malware analysis — malicious · f7c19c2b33e47e2a

MALICIOUS

Office (OOXML) / .XLSX

211.9 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000

MD5: dee6841dad2810dbb7d487803e3f2b4c SHA-1: 952f84f1a308f8f5260558590fe9585863027e8b SHA-256: f7c19c2b33e47e2ab2d742587e9b593ac3d8756caf37c710ae1f2800aeb144a9

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The critical heuristic firing indicates the presence of Excel 4.0 macros. The macro code appears to be attempting to write a file to 'C:\ProgramData\excel.rtf', likely as a staging location for a downloaded payload. The obfuscated nature of the script prevents further analysis of the exact download mechanism or final payload, but the intent is clearly to execute external code.

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.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `f4fd4174fab79141e089ffcba5a0d334d736924431066d5c8ac9cd51c88b6164`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	497296 bytes

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