Office (OOXML) / .XLSX malware analysis — malicious · 427b38de4effe559

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: b1e41cc8007dfac7765d566b9635f68a SHA-1: 9c15326ba43b20a1072627f3c1dc059866b6fdad SHA-256: 427b38de4effe559f60b162ec32ef1dea774c6634837bbafbc987b5cf8964372

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file is an Excel 4.0 macro sheet, identified by the OOXML_XLM_MACROSHEET heuristic. The macro sheet contains obfuscated strings that appear to construct a path to a file named 'excel.rtf' within the 'C:\ProgramData\' directory. This suggests the macro is intended to execute or drop a malicious file from this location, likely as part of a multi-stage attack. The exact execution flow is unclear due to truncation, but the presence of the macro sheet and the constructed path strongly indicate a malicious intent.

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` `10cce13bf4ba05bb83186e205473a0ad3708fc14aad06d51a1fb532896cfae2c`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	279005 bytes

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