Office (OOXML) / .XLSX malware analysis — malicious · 720ac949e6743c94

MALICIOUS

Office (OOXML) / .XLSX

327.5 KB Created: 2021-03-23 13:50:54 UTC Authoring application: Microsoft Excel 16.0300

MD5: 11ae52bd9c6a338582892d1a0e565269 SHA-1: 3b29f297c2abe8208da5071724db6361348d0d17 SHA-256: 720ac949e6743c94b40a02c010489f57696122431ccd4d9ab7a3eee00b8f7a77

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1203 Exploitation for Client Execution

The file is an Excel spreadsheet containing Excel 4.0 macros. These macros are designed to reassemble a payload from split formulas and then execute it using `certutil` to decode and `rundll32` to run the resulting executable. This indicates a downloader or dropper functionality.

Heuristics 2

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.
XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD

An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `c67812df220d2aa4eccc3e5996096e4cca4c5f539f512f706c2fe068dade17cc`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	2660 bytes

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