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

Static analysis result for SHA-256 5f1c9ea3af80c563…

MALICIOUS

Office (OOXML) / .XLSX

128.9 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: a1ec5173da25d60a963050da1a48456c SHA-1: 165e347213b896cc1d8937772ba940ebbb22152f SHA-256: 5f1c9ea3af80c563de5f8c633e805f1ee2e9ee34e4df53d068adcb15b9e6c1eb
180 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

The file contains critical heuristic firings indicating the presence of Excel 4.0 macros and a reassembled payload. The macros appear to be designed to download and execute files from the specified URLs, likely serving as a downloader for a second-stage malicious payload. The specific nature of the payload is not discernible from the provided evidence.

Heuristics 3

  • Excel 4.0 macro sheet (13 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.
  • ClamAV: Xls.Downloader.GreenOffice01220-9937699-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.GreenOffice01220-9937699-0

Extracted artifacts 13

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
08b2a21dfd49ba82acc3e98fa2548503ea70375384baae9690f9b9f92ee72a12
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 363 bytes
xlm_sheet_01.bin
75486df1e8fdc8dfcfa9347e2efdacc8c653c3f2057c715406ef8db6742ee804
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin 632 bytes
xlm_sheet_02.bin
62069c771b71f4e449852a9717d0e3ee529ecca6497ff21cb92f7f53c4d1b43c
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 2766 bytes
xlm_sheet_03.bin
ae5e83e6d426668a5db416906d420732f1fdd9591d423b86f2b9f1dcd9fa44ac
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet3.bin 1619 bytes
xlm_sheet_04.bin
2cd9dbeea24ca020fd0a4017b931dd97c95e7c0ab519355790f0ba447b4a3039
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet4.bin 573 bytes
xlm_sheet_05.bin
5009dc8e79faedbbf6d81cc8ab84c37fddbbf642b83acb0a4f501b89844ac3ca
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet5.bin 618 bytes
xlm_sheet_06.bin
cd13478f2e3c7cf4b2507e646c0ceb5fea3e2f93cca4db2727dc940a10700abb
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet6.bin 766 bytes
xlm_sheet_07.bin
d6cbc03e36305aa993ba351dfcc3c9f2613ba6f5108c24fb559e4b12cff76c9e
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet7.bin 472 bytes
xlm_sheet_08.bin
fe33ad0661ee70bb32c1080c3584fa621afd5781d67903179cd30bf602806937
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet8.bin 423 bytes
xlm_sheet_09.bin
ff4e973b54b80c00d226e9c4a283940eb8435e9810d5d202ee1f5db363852b06
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet2.bin 754 bytes
xlm_sheet_10.bin
6136e300f8261bd0e71a47aed8dd19bafdab22d27cb4eaa966ba836779f08b49
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet3.bin 679 bytes
xlm_sheet_11.bin
46a26398a13684a16d8ede38746c526be4025503508fe8a89a3748973af9a2d3
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet4.bin 799 bytes
xlm_sheet_12.bin
52cbcb9c330923e6a38883615db2b9d510da997b15c7142598ab08d9f0a99559
xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet9.bin 619 bytes