Office (OOXML) / .XLSM malware analysis — malicious · 39a648d2a1e438da

MALICIOUS

Office (OOXML) / .XLSM

353.4 KB Created: 2021-08-09 10:17:00 UTC Authoring application: Microsoft Excel 12.0000

MD5: fc525093844bee676c18d9a5f39d4b00 SHA-1: 450e8a909c6199c9dd04585b4971e540c3024038 SHA-256: 39a648d2a1e438da1c387ee74a304265c3d7c4ca80bbcfcc6ec56b63af312954

210 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Service Execution: Visual Basic T1204.002 Malicious File: User Execution T1059.001 Command and Scripting Interpreter: PowerShell T1059.003 Command and Scripting Interpreter: Windows Command Shell

This XLSM file contains Excel 4.0 macros, indicated by the 'OOXML_XLM_MACROSHEET' and 'OOXML_XLM_AUTOOPEN_DEFINEDNAME' heuristics. The macros utilize dangerous functions such as FOPEN, FWRITE, FCLOSE, EXEC, and REGISTER, which are commonly used to download and execute arbitrary code. The presence of these functions suggests the macro sheet is designed to fetch and run a second-stage payload, likely from a remote source. The 'OOXML_XLM_DANGEROUS_FN' heuristic explicitly flags the use of these Win32 API calling primitives within XLM formulas.

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.
Suspicious extracted artifact medium EXTRACTED_FILE_STATIC_TRIAGE

One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.
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.

Filename	Kind	Source	Size
`xlm_sheet_00.xml` `7aabc549731a17e8ee37f8a27de7a6572c7d2583052641bf2feef6c9278244e6`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.xml	739406 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact contains 1 shell/COM execution token(s).

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