Office (OOXML) / .XLSX malware analysis — malicious · ac7133fa7c21ab84

MALICIOUS

Office (OOXML) / .XLSX

108.7 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000

MD5: 7eed5b6401506aadfaa55ec9ae2a7c51 SHA-1: d695092cd230476747644c7cb96933400ea371ca SHA-256: ac7133fa7c21ab84c34595a9e8ee299342bb9f6a542d33abbc4fb3d5490e0818

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The primary finding is the presence of Excel 4.0 macros, indicated by the OOXML_XLM_MACROSHEET heuristic. While the macro content is truncated and obfuscated, this technique is commonly employed to download and execute second-stage malware. Without further deobfuscation or network activity, the specific family and payload remain unknown.

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` `feccf56d80470195345756290d2f196eb2d8eeb91cfabf2e36dec8a1cb9e1458`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	232855 bytes

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