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

Static analysis result for SHA-256 5dbf7507ae75cbd2…

MALICIOUS

Office (OOXML) / .XLSX

113.6 KB Created: 2021-03-05 04:08:28 UTC Authoring application: Microsoft Excel 16.0300
MD5: ac0b99228647c4be42cabdae9fa0f8a5 SHA-1: 55374aca729f354f3c06ca2b98bad7a4c7b315ab SHA-256: 5dbf7507ae75cbd25993ae3b073890cb0a58082d1d5c2e0bb016196f0c7ffaca
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that are designed to download a DLL payload from the URL http://bfdnews.xyz/campo/e/eC and save it to C:\ProgramData\flotsh\h4gf.dll. This indicates a downloader functionality, likely to fetch and execute further malicious content. The ClamAV detection further supports its malicious nature.

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.
  • ClamAV: Doc.Downloader.Trojan-bf70f023603538ee-bf70f023603538ee-9950269-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Doc.Downloader.Trojan-bf70f023603538ee-bf70f023603538ee-9950269-0
  • 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://bfdnews.xyz/campo/e/eC

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
6fa02d0dfa7bf340a11ee16ee5f8108c84317a0eaf903bb3b0a4017bbc154c7c		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 10168 bytes

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