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

Static analysis result for SHA-256 fc155e6d2cd54391…

MALICIOUS

Office (OOXML) / .XLSM

237.1 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 66cb590b49ddcba75e1ed4647ca3d5f6 SHA-1: d03c9995f6db092ab06de8b57617e43ec64857c2 SHA-256: fc155e6d2cd54391de76ef0716b8b0f9714c22a689c202252ace59ab7bb3cf28
250 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell

The sample is an XLSM file containing Excel 4.0 macros. Critical heuristics indicate the use of dangerous XLM functions like FOPEN, FWRITE, FCLOSE, EXEC, and HALT, which are used to download and execute payloads. The script reconstructs the path 'C:\ProgramData\KVTXZDMqJcxrkMC.sct' and uses FOPEN to open it, likely to write or execute a downloaded payload. This indicates a downloader functionality.

Heuristics 6

  • 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, FWRITE, 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.
  • ClamAV: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0
  • 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://schemas.openxmlformats.org/spreadsheetml/2006/main
    • http://schemas.microsoft.com/office/excel/2006/main
    • http://schemas.openxmlformats.org/officeDocument/2006/relationships

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
1e701afeb920180fea4e9b38e6679bf2a831f4cba069479b06981056205520f8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 745861 bytes

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