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

Static analysis result for SHA-256 76d3787c138d1a1c…

MALICIOUS

Office (OOXML) / .XLSX

291.1 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300 First seen: 2020-12-25
MD5: 629d763d95b87fa7df0b580f3d6a9b7c SHA-1: daee9bf04b6602ef068b0d1325d953fd4ba22858 SHA-256: 76d3787c138d1a1cab7c4ecd2ce7208c5101863864b899b01580e7aa72ba1b41
242 Risk Score

Malware Insights

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

The file contains Excel 4.0 macros, identified by critical heuristics, which are designed to download a payload from the URL https://gts-egy.com/ds/121120.gif using WinAPI functions like DownloadToFileA and ShellExecuteA. The macros are reassembled from CHAR() and split formulas, indicating an attempt to obfuscate the malicious content. This strongly suggests the file's purpose is to act as a downloader for further malicious activity.

Heuristics 5

  • Excel 4.0 macro sheet (1 sheet(s)) critical 3 related findings 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 (1 URL) 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://gts-egy.com/ds/121120.gif Referenced by macro

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
aa42885ece34b2e4ae239ba4933cfce32076ea11a4c91693832c25cc1077750f
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 197211 bytes
Preview script
First 1,000 lines of the extracted script
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... (truncated)