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

Static analysis result for SHA-256 5b10b75c8e445691…

MALICIOUS

Office (OLE) / .XLSX

235.0 KB Created: 2020-05-21 07:44:41 Authoring application: Microsoft Excel
MD5: f0f2762f8306df17e299f773fc02e0c8 SHA-1: adb89d93729621fdc9405309db7e4fd7536561a4 SHA-256: 5b10b75c8e445691f063fb5c7c2a290d5e1cf29f39f88a87c578b61cd2eb3fa9
140 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1566.001 Spearphishing Attachment

The sample contains obfuscated Excel 4.0 macros, including an Auto_Open entry, indicating an attempt to automatically execute malicious code upon opening. The macro uses a complex chain of FORMULA and CHAR functions to construct and execute a payload, likely for downloading and running a second-stage exploit. This is a common technique for delivering malware via spearphishing attachments.

Heuristics 3

  • Excel 4.0 Auto_Open defined name critical OLE_XLM_AUTOOPEN_DEFINEDNAME
    oletools recovered an Auto_Open / Auto_Close entry from an Excel 4.0 macro sheet. The raw BIFF name can be tokenized or partially opaque to byte-string checks, but the recovered macro listing confirms the workbook has an XLM auto-execution entry.
  • Obfuscated XLM Auto_Open execution chain critical OLE_XLM_OBFUSCATED_AUTOEXEC_CHAIN
    Excel 4.0 macro sheet contains an Auto_Open / Auto_Close entry and an obfuscated formula execution chain. The macro builds strings through FORMULA(CHAR(...)), primes state with SET.VALUE / GET.CELL / GOTO, and transfers control through RUN(). This is a high-confidence XLM malware pattern.
  • Excel 4.0 (XLM) macro sheet present medium OLE_XLM_AUTOOPEN
    Workbook contains an Excel 4.0 macro sheet sub-stream — XLM is rarely seen in modern legitimate workbooks and was a major Office malware vector during 2020-2022.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_macros.txt
b78855b2477f4b950a11cb509b43fa1340fa4cf7b4524c9b41f4c703a1bc9544
xlm-macro oletools.olevba.extract_all_macros (XLM macro listing) 129268 bytes