Office (OOXML) / .XLSX malware analysis — malicious · 499f869b93aa412f

MALICIOUS

Office (OOXML) / .XLSX

1.16 MB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-29

MD5: e11d8072bcd027ac94b972b34876ddd0 SHA-1: ec9820bc166de546d8ffc7a4037157667ada8eeb SHA-256: 499f869b93aa412fa94d8a58eb5e72f1041bd41166bd33c5890daab3bbe6b4b0

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file is an XLSX document containing multiple Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. These macro sheets are known to be used for executing arbitrary code. While the specific commands within the macro sheets are heavily obfuscated and truncated in the provided evidence, the presence of these macro sheets strongly suggests an intent to download and execute a secondary payload. No specific family could be identified due to the obfuscation.

Heuristics 2

Excel 4.0 macro sheet (3 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.
XLSB international XLM macro sheet hidden in .xlsx critical OOXML_XLSB_INTL_MACROSHEET_IN_XLSX

OOXML package is named .xlsx but contains XLSB workbook parts and an international Excel 4.0 macro sheet. This hides XLM macro execution from scanners that trust the extension or only inspect XML worksheet parts. The technique is macro execution, not a document-parser CVE.

Extracted artifacts 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`emf_00.emf` `a12daa770fc1848e39c880d90376e8e5b6814576e9bdbfaa076685fd9b9b2ba3`	ooxml-emf	OOXML EMF part: xl/media/image1.emf	6145428 bytes
`xlm_sheet_00.bin` `94dcae400bad291e7734b3303be72f72bc74b4ef3f7737fe960644bb383a7a69`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	484 bytes
`xlm_sheet_01.bin` `6b69a539d2d44586cd29d86a91c29f1e2ba8aa4a323b5a4a9f7f0d23cd002d42`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	484 bytes
`xlm_sheet_02.bin` `46ff111a4683eea3ae97021320d38aa4eb315350d26452c986cde8fd19a80a92`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2165 bytes

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