Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 38f5a4e3d235e904…

MALICIOUS

Office (OOXML) / .XLSX

1.16 MB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-04-18
MD5: 75d6d67b027d0a46b830bc9bb73bd538 SHA-1: b15874653a9e7a8a819c7db7b34b6070cbbbed44 SHA-256: 38f5a4e3d235e9045f23c1acf92fae6faae4ba9da1418cafc26e3f91e170772f
200 Risk Score

Malware Insights

Emotet · confidence 95%

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

The critical heuristic 'OOXML_XLM_BINARY_WINAPI_STRINGS' indicates the presence of Excel 4.0 macros that utilize WinAPI functions like URLDownloadToFileA and CreateDirectoryA. The script content confirms this, showing attempts to create a directory 'C:\Rfgsg' and download files named 'Ojian.ocx', 'Ojana.ocx', and 'Ojanb.ocx' into it, followed by execution via 'regsvr32'. This strongly suggests a downloader mechanism, consistent with the Emotet family, which is also flagged by ClamAV. The embedded OLE object is likely part of the delivery or obfuscation.

Heuristics 4

  • Excel 4.0 macro sheet (1 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.
  • Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS
    Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.
  • ClamAV: Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0
  • Embedded OLE object medium OOXML_OLE_OBJECT
    Document contains an embedded OLE object

Extracted artifacts 4

Files carved from inside the sample during analysis.

FilenameKindSourceSize
ooxml_oleobject_00.bin
91be447cf4ed5b5fa18315c6180ef6d62647686972b570319f960439fe37d717		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject2.bin 3099136 bytes
ooxml_oleobject_00_ole10native_00.bin
a6724425b761391a2288cdb0e402bdc8cf2de9a4e93260c95af92b78344a367e		 ole-package OOXML xl/embeddings/oleObject2.bin Ole10Native stream: Ole10Native 3072068 bytes
emf_00.emf
3f0f6bb70f3d65dcc8d248d78ac320bcc22b1148ea5fdd2c1043065d03460133		 ooxml-emf OOXML EMF part: xl/media/image1.emf 6144552 bytes
xlm_sheet_00.bin
83397e9001624bdedd85e47d3086368ce2232893d46fc419bbd30d9c3ba1953a		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 2021 bytes

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