Office (OOXML) / .XLSX malware analysis — malicious · baab29facbc4a535

MALICIOUS

Office (OOXML) / .XLSX

125.2 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300

MD5: 071fdb3cd239730c723d98be3aa35b31 SHA-1: bb05b0fd3173ae3438f9862c705f56c38bd72a08 SHA-256: baab29facbc4a53525b3b674c823217b4c1b82620dc244010f92a8dbd133436c

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications

The sample is an XLSX file containing multiple Excel 4.0 macro sheets, as indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The ClamAV detection 'Xls.Downloader.GreenOffice01223-9937701-0' strongly suggests a downloader functionality. Although the macro content is truncated and obfuscated, the presence of multiple macro sheets and the downloader signature point to an attack pattern where the file's primary purpose is to fetch and run additional malicious code.

Heuristics 3

Excel 4.0 macro sheet (8 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.
ClamAV: Xls.Downloader.GreenOffice01223-9937701-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Xls.Downloader.GreenOffice01223-9937701-0

Extracted artifacts 8

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `83293298284ab7ada3395ede87ce17b984c0619e14c370ed88feed58dd4e7dfe`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	2134 bytes
`xlm_sheet_01.bin` `32a6d2b55dcef01bc5bfe7c8a1908945c916ea744417a6ef344ccfff09442b2a`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	428 bytes
`xlm_sheet_02.bin` `2be5644cf290b095c4031254929a99beb39c89619d1a54e7b3894b117384b5b7`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	428 bytes
`xlm_sheet_03.bin` `3f2bcb2113bedfa0fccb584ca0134147981b280b9757c8f303099217e26f9572`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet3.bin	428 bytes
`xlm_sheet_04.bin` `2b3737a79d4a18b154ff1da7faf504ec53e460446a7609e6f2cdc408dd88e656`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet4.bin	428 bytes
`xlm_sheet_05.bin` `427a21db45774f581eb1d16d91d217106cd62ed6544328aa2331419c4cb4b386`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet5.bin	428 bytes
`xlm_sheet_06.bin` `8950a673116dde1436ab1134b3912bcfce71a156a297474fe200ae255a983ce6`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet6.bin	428 bytes
`xlm_sheet_07.bin` `90beff7f8a332f68f762ee0fddb282ffe1d0216ddbe6d633ec257cca69c4f513`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet7.bin	428 bytes

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