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

Static analysis result for SHA-256 80bc81de2be6219e…

MALICIOUS

Office (OOXML) / .XLSX

59.9 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 0bbe845ee3a89a430639d060192c322e SHA-1: 53ba743e77e0ec68d37c80daef0b30715e1f42f7 SHA-256: 80bc81de2be6219ed2def0cbbd5055536e913d51d115b1f7554d88a908c81b72
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution T1105 Ingress Tool Transfer

The sample contains Excel 4.0 macros that reconstruct a command to execute 'mshta C:\ProgramData\excel.rtf'. This command is designed to download and execute a payload from one of the three provided Discord CDN URLs. The use of XLM macros and the command execution pattern are indicative of a downloader.

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), 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 https://cdn.discordapp.com/attachments/907666907405099111/907967563433148436/vJKLRLAqBMY.mov
    • https://cdn.discordapp.com/attachments/907665395815677994/907970247053688892/vJFjgo.mov
    • https://cdn.discordapp.com/attachments/907666907405099111/907967419908255764/KmylGRMpPBz.mov

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
9a59d31bf11f4c5a9f2c309273d9f0f22bd914a16047a37d62df9a8d459411d5		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 62648 bytes

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