Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 8c5b8f35519da2e7…

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: e43a7367bda369e965e3be549cf6e6ee SHA-1: f18ea8aab52ff4740d270eeb2a8d499c9888d29e SHA-256: 8c5b8f35519da2e7c5f3281b6f67bb0b1479ab5b5ba7608baf2c92dac87411cd
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer

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 'URLDownloadToFileA' and 'ShellExecuteA'. The reconstructed URL 'http://tai.ie/21.gif' is likely the source of the 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://tai.ie/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: 93f82cd6152f068994220ca0f380c49956636a00761b82bbbbb5b9f72a904fde
Preview script
First 1,000 lines of the extracted script
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... (truncated)

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