Office (OOXML) / .XLSX malware analysis — malicious · ec78734f010ae101

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 9a33884f58fec9cd6ffb0d82652d8874 SHA-1: 21a209b1eef5af8ac31ba784f10aca0c37e7760b SHA-256: ec78734f010ae101fa12c9ead87f81833fffbb291ddd858da8eaa240d62b8f59

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The critical heuristic firing indicates the presence of Excel 4.0 macros within the XLSX file. Analysis of the macro sheet reveals a suspicious path, 'C:\ProgramData\fnsfunSfgRgnKjFsgNd\rtf', which is likely used to stage or execute a downloaded payload. The macro's intent appears to be the execution of arbitrary commands, consistent with a downloader or initial access stage.

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` `dbadaa6d8364d36b8efb984a902278bab9877c1d3668bc6550c38e4cb08202d7`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	4440 bytes

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