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

Static analysis result for SHA-256 2131544f0cfa54af…

MALICIOUS

Office (OOXML) / .XLSX

90.1 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 6b7bad3cea00c7bc8af7e7d0143c5928 SHA-1: 8c8c8bfe0d0f61dec2a2083488ff709555b79f0a SHA-256: 2131544f0cfa54af9bdd61cd990af05f1a4483df67d6e6d76ece14cb9cc550f6
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that utilize WinAPI functions such as URLDownloadToFileA to download files from provided URLs. The macros appear to be designed to fetch and execute a secondary payload, indicated by the presence of download strings and the overall malicious verdict. The URLs extracted, while currently flagged as benign, are the likely sources for the second-stage malware. The obfuscated nature of the macro content prevents a more detailed analysis of the exact execution flow.

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/911249881849536584/912356063758675998/GjEdowscAmeMpshekniggagook.flac
    • https://cdn.discordapp.com/attachments/911249881849536584/912356058922614854/CVjrWfYwLXUpshekniggagook.flac
    • https://cdn.discordapp.com/attachments/911249881849536584/912356067688714250/cvVactCffEgjaSvpshekniggagook.flac

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
55c22c36d1aeeb228c869a497d582ebd572b5fd4c47c5bb6a8b38a2e4a5650d9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5255 bytes

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