Office (OOXML) / .XLSX malware analysis — malicious · 19de42df539046cc

MALICIOUS

Office (OOXML) / .XLSX

26.4 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300

MD5: e8420d5d5cb4a0598a200627b9a66772 SHA-1: 6b03bd2aa256d7682f3e8cf93a812394cca3d7b2 SHA-256: 19de42df539046cc8716d5d71554eae3cc1a3726f90a63de87c3033d9cd24baf

182 Risk Score

Malware Insights

MITRE ATT&CK

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

The file contains Excel 4.0 macros, indicated by the OOXML_XLM_MACROSHEET heuristic. These macros utilize WinAPI functions such as URLDownloadToFileA and ShellExecuteA, as identified by OOXML_XLM_BINARY_WINAPI_STRINGS. The primary goal appears to be downloading and executing a secondary payload from the URL https://revistascientificas.posgradocolumbia.edu.py/ds/3.gif, as evidenced by the OOXML_XLM_CELL_ARRAY_URL firing. The macro sheet itself is heavily truncated, but the presence of these functions strongly suggests a downloader or droppper functionality.

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. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS

Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.
URL reconstructed from XLM cell array (1 URL) critical OOXML_XLM_CELL_ARRAY_URL

Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string cells in both row-major and column-major order.
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 https://revistascientificas.posgradocolumbia.edu.py/ds/3.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `4be47f6fcaf3ddcd2c09a8b9ee903affb3f4991b54c12b0197126fd22afb2207`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	200547 bytes

Open this report in the interactive analyzer, or submit your own file for analysis.