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

Static analysis result for SHA-256 c3755319c42781c2…

MALICIOUS

Office (OOXML) / .XLSX

74.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 9cd0a129f9b88ab103b36ad148750daa SHA-1: d829400eb7589023612a20fb706be73ab37c62af SHA-256: c3755319c42781c294353006ba9bf591b19a42295e411aa71f23c6ff98c14b7e
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The file contains Excel 4.0 macros that utilize WinAPI functions such as URLDownloadToFileA to download content from URLs. The reconstructed URLs point to executable files, suggesting the macro's intent is to download and execute a second-stage payload. The macro sheet also contains strings related to sending reports to Microsoft, which is a common lure in phishing documents.

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

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
95ce551c90f05c4927442b8d640b2b8be968412023e9be05d08b48fb41f313c0		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5737 bytes

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