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

Static analysis result for SHA-256 cdd7f92b94aa50ed…

MALICIOUS

Office (OOXML) / .XLSM

131.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: d5559cc7515ebc4559dc2bd67efa624e SHA-1: 975307366120d48854b4ef3ba3c9fea5b865d8cd SHA-256: cdd7f92b94aa50edb4dd46f7a31faa765dcac8bfe641ccb6053851b4ae649f28
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic for Applications T1204.002 Malicious File T1059.001 PowerShell T1105 Ingress Tool Transfer

The file is an XLSM document containing Excel 4.0 macros. The macros utilize dangerous functions like FOPEN, FWRITE, and EXEC to download and execute a second-stage payload. Specifically, the FOPEN function is used to open a file at 'C:\ProgramData\zZ', and the EXEC function is likely used to run the downloaded payload. The reconstructed URL 'http://193.55.46.0:5848/mf' is used for downloading the payload. The presence of these functions and the embedded URL strongly indicate a downloader or droppper functionality.

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: FOPEN, FWRITE, 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.

FilenameKindSourceSize
xlm_sheet_00.xml
61501cd4058193d798528ac36619c25a75f8cb1fabf63de3bc8a28008d096832		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5184 bytes

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