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

Static analysis result for SHA-256 5a57cfde14f90fc9…

MALICIOUS

Office (OOXML) / .XLSX

64.5 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: e3b213f2470d2d56bba276efb815ac94 SHA-1: 7399d621e70ec81d0d2a12cf4681ac8036cb624e SHA-256: 5a57cfde14f90fc9402104b82803b9ac6378c3e29a962ae3175a45fc75226782
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

The sample contains Excel 4.0 macros that reassemble a command to execute 'mshta C:\ProgramData\excel.rtf'. This command is likely used to download and execute a second-stage payload from one of the embedded URLs. The macros also contain multiple URLs pointing to .wav files, which are likely disguised payloads.

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.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • 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/906978504971792388/907257694845550632/NLhvmp.wav
    • https://cdn.discordapp.com/attachments/906973832164827169/907255585597186078/Gfrejk.wav
    • https://cdn.discordapp.com/attachments/906978504971792388/907257585080602674/lvMxiLuAZM.wav

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
bfc1ca1e3dc5cde192423ee7b061551c61cbaea9145361ea61fc89954078bb62		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 64787 bytes

Open this report in the interactive analyzer, or submit your own file for analysis.