Office (OOXML) / .XLSX malware analysis — malicious · 1a2fb4aff95a98ba

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: baf684cd508d3707cc14227c878fb346 SHA-1: 7b4b7b5ebf1299a9104efa4be0da967232ccdebc SHA-256: 1a2fb4aff95a98ba3dc91ffbb03f611154ac076ffa6ae96fe5778af1be1bc100

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.003 Windows Command Shell T1218.010 System Binary Proxy Execution: Windows Management Instrumentation

The sample is an Excel 4.0 macro sheet, which is a strong indicator of malicious intent. The macro sheet contains obfuscated commands that, when deobfuscated, reveal a WMI call to execute 'mshta' with a specific RTF file located in ProgramData. This suggests the macro is designed to download and execute a second-stage payload from the specified RTF file, likely leading to further malicious activity.

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` `ab660554048a86dd9c8375ce1d3b49acaee7566e527861da92215397d2980310`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	162073 bytes

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