Office (OOXML) / .XLSM malware analysis — malicious · 1e66c639f157fa06

MALICIOUS

Office (OOXML) / .XLSM

41.3 KB Created: 2020-12-07 14:38:21 UTC Authoring application: Microsoft Excel 16.0300

MD5: 032734a3c93c44855955d4769b7ded98 SHA-1: f38cd18659e0fb5d862bac1d9f24691dda4a292c SHA-256: 1e66c639f157fa066c2e4070a46cb0af32548f4fba63684120513433059cd26d

210 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1059.001 PowerShell T1059.003 Windows Command Shell T1566.001 Spearphishing Attachment T1204.002 Malicious File

This XLSM file contains Excel 4.0 macros that leverage dangerous functions like RETURN() to execute arbitrary code. The VBA script appears to be obfuscated but contains calls that suggest it attempts to download and execute a second-stage payload. The use of Excel 4.0 macros and the obfuscated VBA points to a downloader or initial access mechanism.

Heuristics 6

VBA ActiveX event runs worksheet-decoded XLM formulas critical OLE_VBA_ACTIVEX_XLM_CELL_STAGER

VBA code attached to an ActiveX/UserForm event reconstructs formula text from worksheet constants using Split/Replace/Mid or character shifting, then executes it through ExecuteExcel4Macro or Run. This is a high-confidence malware stager that hides XLM formula execution in sheet cells; it is not a document-parser CVE.
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 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
- http://schemas.openxmlformats.org/markup-compatibility/2006
- http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac

Extracted artifacts 4

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`macros.bas` `2fbb14cb66a1e24a4f8e68fc503721563bb12df9ff3e81ae3f88023d09dcf4be`	vba-macro	oletools.olevba.extract_macros (decoded VBA source from OOXML)	1831 bytes
`vbaProject_00.bin` `9dd6827b7062d4e9d92abb1cdfc3ccfc704348bef41ed37995e67d4b6d72348f`	vba-project	OOXML VBA project: xl/vbaProject.bin	18432 bytes
`emf_00.emf` `da935e8d60e93e41bcd7c3fbb1750ef3ac471c3af78afc8945dfbf31eb54a1e1`	ooxml-emf	OOXML EMF part: xl/media/image1.emf	1408 bytes
`xlm_sheet_00.xml` `2b22e750932dab4395a034bb21fc6fc762875f05072e9861cec551e66d6f3c07`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.xml	1026 bytes

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