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

Static analysis result for SHA-256 bc1d978695e3dc16…

MALICIOUS

Office (OOXML) / .XLSM

73.2 KB Created: 2021-02-08 11:19:03 UTC Authoring application: 16.0300
MD5: 20f9a7843d3f358a6ecfd6dd828cdd6d SHA-1: 9a9b0eb8265cb116bb5bf9e1e1aa29f6ac6b621a SHA-256: bc1d978695e3dc1666923fa13de923870a7604375d57bb6771e2f4bcd8ae8d56
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

This XLSM file contains Excel 4.0 macros that leverage the dangerous `RETURN()` function, indicating an attempt to download and execute a payload. The `URLDownloadToFileA` function is explicitly called, suggesting the macro's primary purpose is to fetch and run a secondary malicious file from a remote source. The presence of hidden sheets and the use of XLM macros are common techniques for obfuscating malicious activity.

Heuristics 6

  • URLDownloadToFile in VBA critical OLE_VBA_DOWNLOAD
    URLDownloadToFile in VBA
  • 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.
  • Dangerous XLM formula APIs: RETURN 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.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains vbaProject.bin — VBA macros present
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 3 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
    • http://schemas.openxmlformats.org/markup-compatibility/2006
    • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
006c18e526e3f3af0b69a0fc459573c36475db3268657a1c443207bb64073d30		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 3528 bytes
vbaProject_00.bin
00f0a17b55e1f72ab441e75a76cec09c8029d5a3dfe887636205f248919d1b96		 vba-project OOXML VBA project: xl/vbaProject.bin 22528 bytes
xlm_sheet_00.xml
34eb1b7dff46fd3d78d4f7acbb9b7827b3cd65da18e69043b56ccce7562253b0		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1022 bytes

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