Office (OOXML) / .XLSX malware analysis — malicious · 2a046ad862cf2c7f

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: abec4df88b31f733fa7af25e1650cc77 SHA-1: 5e85c7f12ab3fc7a47f6df8a3db2756c711c3d66 SHA-256: 2a046ad862cf2c7f7e323fe9d3ea6b1a5870dd6113df67182c2f6dbc7b0d9bde

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

The sample contains Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The macro sheet `xlm_sheet_01.bin` explicitly contains URLs and the string 'URLDownloadToFileTo'. This indicates the macro's intent is to download files from these URLs, likely to execute a second-stage payload. The ClamAV detection of 'Xls.Downloader.Docusign112101-9908076-0' further supports this downloader functionality.

Heuristics 3

Excel 4.0 macro sheet (2 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.Docusign112101-9908076-0 critical CLAMAV_DETECTION

ClamAV detected this file as malware: Xls.Downloader.Docusign112101-9908076-0

Extracted artifacts 2

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `463f81ea38e1a54b35e10a38092cd530cabd5dd29d0b64519809f3285e8a1683`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	363 bytes
`xlm_sheet_01.bin` `55be17aab77b2c6d09c4fbbfd75f1a3e78ca23cab182fdec8ec5708f5c4edc47`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	2879 bytes

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