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

Static analysis result for SHA-256 545b7d7a2d323497…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: f99cdca53282e5d0c5e0a830e6e7439b SHA-1: 5a56ce66d04569464fc73722a1c52c2647ebf2bf SHA-256: 545b7d7a2d32349779c373c2c72c31612353ba8d7c176bb8b6cc560776e655a2
120 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. Heuristics indicate the presence of WinAPI calls related to downloading files and executing them, specifically URLDownloadToFileA, DownloadToFileA, and ShellExecuteA. This suggests the macro's purpose is to download and execute a second-stage payload from a remote location. The specific URLs and executable paths are not fully extractable due to truncation, but the WinAPI functions themselves are strong indicators of malicious intent.

Heuristics 2

  • 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.
  • 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.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
99a6a52acb8f5c734f6d86faf89e0637a94ac99f953aa583d2658b47d2e1f9b9
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 194023 bytes