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

Static analysis result for SHA-256 681773659769266b…

MALICIOUS

Office (OOXML) / .XLSM

247.3 KB Created: 2021-10-06 04:58:13 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2021-10-11
MD5: 2883ddc15cb53aacd5249a0736a750ef SHA-1: d01760509ef0a7b484cfd729948f10ea993c3013 SHA-256: 681773659769266b5f00f6310153683a930d6eab416a24f450e413d2f77c113f
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution T1105 Ingress Tool Transfer

The sample is an XLSM file containing Excel 4.0 macros, specifically utilizing the Auto_Open function. Critical heuristics indicate the use of dangerous XLM formula APIs like FOPEN, FCLOSE, EXEC, and HALT, which are used to download and execute payloads. The macros construct a path to write a VBScript file and then likely execute it, as evidenced by the embedded URL http://gombar.hu/a2.exe.

Heuristics 5

  • 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.
  • Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
    Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
  • Dangerous XLM formula APIs: FOPEN, FCLOSE, EXEC, HALT critical OOXML_XLM_DANGEROUS_FN
    Excel 4.0 macro sheet uses formula APIs that call directly into Win32 (=CALL/=EXEC/=REGISTER/=FORMULA). These are the primitives used to download payloads, write files, and start processes from an XLM macro without invoking VBA.
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 1 hidden sheet(s) — hidden sheets are commonly used to conceal macro code, staging data, or intermediate payload construction
  • 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://gombar.hu/a2.exe
    • http://schemas.openxmlformats.org/spreadsheetml/2006/main
    • http://schemas.microsoft.com/office/excel/2006/main
    • http://schemas.openxmlformats.org/officeDocument/2006/relationships
    • http://schemas.openxmlformats.org/markup-compatibility/2006
    • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac
    • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
    • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
8ca1addede531debe99f13184fa05963df4914847a0ebac1be8c20c17ac250b8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5282 bytes

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