Office (OOXML) / .XLSX malware analysis — malicious · 31cf9135bd6e57bb

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 1a11d57f8ddbc164f7faea072a8f0cea SHA-1: f5e4000fe296871eb42ddc54acef358f029511a5 SHA-256: 31cf9135bd6e57bb20d7891a65c235f033d74fb201424b9064a5b9ed0ae7ae5f

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 that utilize WinAPI functions like URLDownloadToFileA to download a file. The macro reconstructs a URL from a cell array, which is then used to fetch a payload. The script's intent is to download and execute a second-stage payload from the provided URLs. The URLs themselves are reconstructed from the macro's cell array.

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 (3 URLs) 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://cdn.discordapp.com/attachments/910251809556271117/912318020003692574/FqtFBvEOrukvcuntfuck.mp4
- https://cdn.discordapp.com/attachments/910251809556271117/912318007320145940/XOftdbhXmOZcuntfuck.mp4
- https://cdn.discordapp.com/attachments/910251809556271117/912318014416912415/XOwuRIcuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `d37299f4f5a1c881440852ceb148e5ba683a8758cfea14d29ad620a1568b0fcd`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	5593 bytes

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