Office (OOXML) / .XLSM malware analysis — malicious · 16cb141bbfcd56ed

MALICIOUS

Office (OOXML) / .XLSM

113.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000

MD5: 1035dbcb557c7723bf66b5e205e30669 SHA-1: da3e1d8717667d85b84f870ac2434a1c834ae5ec SHA-256: 16cb141bbfcd56edd993b397ec0ce8d56e204656190c7974faf157eaa94d5ce4

130 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. These macros utilize dangerous functions such as FOPEN, FWRITE, FCLOSE, EXEC, and RETURN, which are indicative of malicious activity. Specifically, the FOPEN function is used to construct the path 'C:\ProgramData\TwAi.vbs', suggesting the creation of a Visual Basic script for further execution. The presence of these functions and the constructed file path strongly suggest an attempt to download and execute a second-stage payload.

Heuristics 4

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: FOPEN, FWRITE, FCLOSE, EXEC, 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.
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` `d87f26fbaf4ac9ef65699012a3846c7ae6846eff69bdcaa70c40a9ce25efeb67`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.xml	5265 bytes

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