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

Static analysis result for SHA-256 f1e3a7836cb2d505…

MALICIOUS

Office (OOXML) / .XLSX

84.4 KB Created: 2020-05-21 11:42:43 UTC Authoring application: Microsoft Excel 16.0300
MD5: b6fa82bbe8c8a2beaf381ee7d4178ecd SHA-1: 89cbb4c5efc41cfdae3fc60f5ff9db00d1f6ae59 SHA-256: f1e3a7836cb2d505541e09afde30fc1d651ab4402eca3f8f76bd9d3fa646a553
80 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell

The critical heuristic firing for 'OOXML_XLM_MACROSHEET' indicates the presence of Excel 4.0 macros. Analysis of the 'xlm_sheet_00.bin' content reveals commands that construct paths like 'C:\Users\Public\ngs.txt' and 'C:\Users\Public\ngs.dll'. It also shows the use of 'certutil.exe' to decode a file and 'rundll32.exe' to execute a DLL, suggesting a download and execution chain. The VBA macros are present but truncated, preventing a full analysis of their specific actions.

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.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains vbaProject.bin — VBA macros present

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
7aa4187706b7003a52de6699ad5a674e6d1dfb6921f74ab806ef136961c522e6
vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 2610 bytes
vbaProject_00.bin
a1f6e466940ef460528067345798237ed185ae05caf8f6c82185138081665737
vba-project OOXML VBA project: xl/vbaProject.bin 23040 bytes
xlm_sheet_00.bin
c793a285c4dad4be43c75d6b40d6fcb36933aeabb2c2a05f8246e4c3ae9713ac
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 1903 bytes