Office (OOXML) / .XLSX malware analysis — malicious · 55387351559fca53

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: e59387c1bec6dc3ca912d5c4168480ed SHA-1: 77eecb292a588a15778b4abe3b8244829835b659 SHA-256: 55387351559fca536ed4b88091f68a39304da9dae1a01d5f1bd8461f23034942

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 sheet contains obfuscated commands that appear to construct a path to a file in the Startup directory, likely for persistence. The reconstructed path is C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\Rjrt.rtf. This suggests the macro's primary purpose is to download and execute a second-stage payload, establishing persistence on the compromised system.

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` `5564f0c2ab567e78c825ac797b8b37e40aafcc50c3eb9db31d7ed6917cce9f38`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	7732 bytes

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