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

Static analysis result for SHA-256 6776f7754612a477…

MALICIOUS

Office (OOXML) / .XLSX

70.6 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 5dd0de7ff868120676ac10f9bd43b1b1 SHA-1: 253a83e88e2b3ced6e31e83bf61c86d50bf5ebf2 SHA-256: 6776f7754612a477eb7f3edc596f4e58b62638dcb90e196f9c0e372c1a09bcbc
242 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that utilize WinAPI functions like URLDownloadToFileA to download a file. The macro reassembles a command to execute 'mshta C:\ProgramData\VboNxrUgMyVCjK.rtf', indicating it attempts to download and run a second-stage payload. The extracted URLs are likely sources for this payload.

Heuristics 5

  • 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.
  • 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 http://103.117.180.99:8080/PJ3ZQWVJPYCYDCA9A6Q2Y6YAC
    • https://cdn.discordapp.com/attachments/910251809556271117/912318014416912415/XOwuRIcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318020003692574/FqtFBvEOrukvcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318007320145940/XOftdbhXmOZcuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
d889c8405c6b8b4a47618fb7a9cda1a64914c2b2d0a1ae79fe0e49d541f913a0		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5703 bytes

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