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

Static analysis result for SHA-256 b9dd8991b62a9b5a…

MALICIOUS

Office (OOXML) / .XLSX

66.6 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: ee20db6d490ae38a0dd08d5c7a81b411 SHA-1: 585bc762eb3ee0ffaf3df45290093cca63b5aed2 SHA-256: b9dd8991b62a9b5a572a9fe460984afb74e7c51214a9337e02566567028dfd6e
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that utilize WinAPI functions such as URLDownloadToFileA to download files from the provided URLs. The macros are designed to download and execute a second-stage payload. The URLs, while marked as confirmed benign by the analysis environment, are still considered IOCs due to their use in the macro's download functionality.

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.
  • URL reconstructed from XLM cell array (3 URLs) critical OOXML_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. 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 cells in both row-major and column-major 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 https://cdn.discordapp.com/attachments/911249881849536584/912356067688714250/cvVactCffEgjaSvpshekniggagook.flac
    • https://cdn.discordapp.com/attachments/911249881849536584/912356063758675998/GjEdowscAmeMpshekniggagook.flac
    • https://cdn.discordapp.com/attachments/911249881849536584/912356058922614854/CVjrWfYwLXUpshekniggagook.flac

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
3c31db472126bffe02d28431a1a51d770f60412f62a72a844624d96b892d781e		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5071 bytes

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