Office (OOXML) / .XLSM malware analysis — malicious · 98d9bf0e52d0dd57

MALICIOUS

Office (OOXML) / .XLSM

33.6 KB Created: 2021-01-25 13:44:30 UTC Authoring application: 16.0300

MD5: 127679ab38ebc3fa96c34792561f85ba SHA-1: 95f8cbb52a3e6dd525b26d6f3b4f378b22f261d4 SHA-256: 98d9bf0e52d0dd5744a283db292239230c072e541b6edb0b0eb6b53265bf3667

210 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1059.001 PowerShell T1204.002 Malicious File T1105 Ingress Tool Transfer

This XLSM file contains Excel 4.0 macros, which are known to be used for malicious purposes. The critical heuristic 'OOXML_XLM_DANGEROUS_FN' indicates the use of dangerous XLM formula APIs like RETURN, which can be used to download and execute payloads. The script also contains a call to URLDownloadToFileA, a function commonly used to download second-stage malware. The presence of hidden worksheets further suggests an attempt to conceal 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.

Filename	Kind	Source	Size
`macros.bas` `a652d0d3f42148eea89b9286cd065ee54cf4691e49715df528c29f104f96a367`	vba-macro	oletools.olevba.extract_macros (decoded VBA source from OOXML)	3441 bytes
`vbaProject_00.bin` `3d33d68d167a9a08bffb9a7308165f3146e5ab004cc605e22180441b6183b766`	vba-project	OOXML VBA project: xl/vbaProject.bin	23552 bytes
`xlm_sheet_00.xml` `e7f433b9b6ff773d85557baf829f63d74cdd398afd824a77b694235dc76c1c2f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.xml	980 bytes

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