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

Static analysis result for SHA-256 6ebd8de97e693bfd…

MALICIOUS

Office (OOXML) / .XLSX

113.6 KB Created: 2021-03-05 04:08:28 UTC Authoring application: Microsoft Excel 16.0300
MD5: be4309ece0c0f1f15119b8edec5c56aa SHA-1: 4a3f877d2d685fd9310b39f62632d6dd40a59b6f SHA-256: 6ebd8de97e693bfd9cb1c21d085e39869ca2c0be0a46b7a389194c7cc6b1ba05
182 Risk Score

Malware Insights

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

The file contains Excel 4.0 macros that are reassembled from CHAR() and split formulas. These macros 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 leading to further malicious activity.

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
5f2a2f63fd0eb333b35972b06bcb6b07010281e8798e7327475695a27fdb4265		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 10168 bytes

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