Office (OOXML) / .XLSX malware analysis — malicious · 4c2d9a490d0f7d99

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 4b83ca0bd53d4c9165e61a1cc8411a4e SHA-1: 349d3543ce61727365b4c1dce11518bdbf309550 SHA-256: 4c2d9a490d0f7d99217e5b7f6cdf5e18a4fca020db6d89592574db2f3df60db5

180 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

The sample contains embedded Excel 4.0 macro sheets, identified by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. The macro content includes strings that reconstruct URLs and filenames, indicating a downloader functionality. Specifically, the macros appear to construct URLs such as '190.14.37.153/', '192.99.255.41/', and '80.71.158.163/' and target files named '.dat' and '.dat2', suggesting the download and execution of a second-stage payload.

Heuristics 3

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.
ClamAV: Xls.Downloader.Docusign112101-9908076-0 critical CLAMAV_DETECTION

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

Extracted artifacts 3

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `fc3749e4f74c1293dc36bc33bfc5481e4492838facad05a8af43cdfe54377654`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	541 bytes
`xlm_sheet_01.bin` `906cf334b7e575a580033e8d27ae5eb97f0a225a66ed59706e9821a3ca37d9fd`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	1814 bytes
`xlm_sheet_02.bin` `8f8bc19938c9a024a8b6ba22e84df50cac24fa8598bb733c13886a2e23616945`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	1716 bytes

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