Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 75c9855148111e0f…

MALICIOUS

Office (OOXML)

746.5 KB Created: 2020-05-11 14:19:29 UTC Authoring application: Microsoft Excel 15.0300 First seen: 2020-12-25
MD5: 0f6debb0f739f5f9f0f8cc8634ec5614 SHA-1: cf553d81ca5617680bcc47c094f670e94f75f182 SHA-256: 75c9855148111e0f3b8f2520a289d10aa63b2d00eb305d6314d8bb4a31121ad8
182 Risk Score

Malware Insights

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

This Excel file contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros contain strings indicative of downloading and executing a file, specifically referencing WinAPI functions like URLDownloadToFileA and ShellExecuteA. The embedded URL http://auroom24.ru/21.gif is likely used to fetch a second-stage payload.

Heuristics 4

  • Excel 4.0 macro sheet (1 sheet(s)) critical 2 related findings 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.
  • URL reconstructed from XLM cell array (1 URL) critical OOXML_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell), inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation, or split across multi-char fragment cells a download formula concatenates by reference (=A1&A2&… / CONCATENATE(...)). The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string/shared-string cells in row-major and column-major order plus FORMULA cell-reference concatenation in token order.
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL http://auroom24.ru/21.gif Referenced by macro

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 53822 bytes
SHA-256: fe0aa14746d3ee2587c87bd4b45cb43220e051b210ece0cfe9ff493d73611ca2
Preview script
First 1,000 lines of the extracted script
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... (truncated)

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