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

Static analysis result for SHA-256 61005cab010bde97…

MALICIOUS

Office (OOXML) / .XLSM

204.5 KB Created: 2021-08-26 06:04:04 UTC Authoring application: Microsoft Excel 16.0300
MD5: 54c351236ba33c74a10f1fcccf81b4fd SHA-1: fa734041869ffc2e811aaaf6ee5e9d26f196e53f SHA-256: 61005cab010bde9798cb5c7ee05497c08ba71d638644f05a1b5e58c8eac67ca1
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. The macros use the `REGISTER.ID` function to call `ShellExecuteA` and the `CALL` function to execute a PowerShell command. This PowerShell command downloads a file named `remit.exe` from `http://192.210.214.221/remit.exe` to the public user directory, renames it to `filesvr.exe`, and then executes it. The use of `CALL` and `REGISTER.ID` with dangerous functions indicates a high likelihood of malicious intent.

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: CALL, 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://192.210.214.221/remit.exe
    • http://ns.adobe.com/xap/1.0/
    • http://www.w3.org/1999/02/22-rdf-syntax-ns#
    • http://ns.adobe.com/iX/1.0/
    • http://ns.adobe.com/xap/1.0/mm/
    • 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
9b172cfe4618679ea48a8d1d88cd9f8c14c0da7bc512e4cfbeb4130df324fe94		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1935 bytes

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