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

Static analysis result for SHA-256 19a8a28e3626a6d5…

MALICIOUS

Office (OOXML) / .XLSX

68.5 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: af37986b897322e6888efa0a4428c883 SHA-1: 6f66fc6d8d4913b11e4982a50658eca42b42f98b SHA-256: 19a8a28e3626a6d58fdc499b95c35cb9d7ec2ae4cdcefd3460d4b40b868d369b
182 Risk Score

Malware Insights

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

The sample is an Excel file containing Excel 4.0 macros. These macros are designed to reassemble a payload from CHAR() and split formulas, ultimately executing commands like 'wmic roesscall cree mshta C:ProDatywSkSCmKwKtf'. The macros also reconstruct and reference three URLs hosted on Discord's CDN, which are likely used to download and execute a second-stage payload. The use of XLM macros and the download-and-execute pattern are indicative of a downloader malware.

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.
  • 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/912720368844824620/913069632129212466/reSCeFOYjZtCtkOyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069669341069452/jPzSCuyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069652077326346/KftJXyrZQyellowfacebrownietacohead.ogg

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
92bf8cc331ea462307986a5e4121777486534ee852598811dd746bdfea1d0d27		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 7744 bytes

Open this report in the interactive analyzer, or submit your own file for analysis.