Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 d82fa52fff66e4df…

MALICIOUS

Office (OOXML) / .XLSX

97.1 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: 63a53bd8dcd47142f4c6a23bfca2e611 SHA-1: fe51d30509c213a2fc2264b32805ce774121d54a SHA-256: d82fa52fff66e4df950bbb43e387d2b0128c479c3fdcfefcd98d9c3f1cece5c6
240 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample contains Excel 4.0 macros, identified by the OOXML_XLM_MACROSHEET heuristic. These macros are designed to download and execute payloads from URLs such as 'http://C:\ProgramData\Volet1.ocx', 'http://C:\ProgramData\Volet2.ocx', and 'http://C:\ProgramData\Volet3.ocx'. The script also uses 'regsvr32' to execute these downloaded OCX files, indicating a downloader and execution attack pattern.

Heuristics 4

  • 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.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • 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.

FilenameKindSourceSize
xlm_sheet_00.bin
30e7f1eb7b7cda9226667aa44630e34cb4e61815c9b73ffde1c06f2d016d24d9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 363 bytes
xlm_sheet_01.bin
924c95acbe52d08cb50364609116239c27cf91b6440c18d7744972648a370d60		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 2900 bytes
xlm_sheet_02.bin
e80c1b37f3c5cec1142f106d8141d8a69bae7bc3fbf9a747d153a562b95978ef		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin 1676 bytes

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