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

Static analysis result for SHA-256 29e84b1c9c4a0bb8…

MALICIOUS

Office (OLE) / .XLSX

298.5 KB Created: 2021-10-27 10:31:49 Authoring application: Microsoft Excel
MD5: c0bff0b73581e6c39ef7dbe6f12c1403 SHA-1: b723107593ee808ff71245df8de3cbfddf95f02e SHA-256: 29e84b1c9c4a0bb841304879a3e5cceda1331e41bf97313032a12e17bfa4613a
202 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1204.002 Malicious File

The sample contains Excel 4.0 macros, including an Auto_Open entry, which is a critical finding. The macros construct and display an error message to the user, likely as a distraction. Crucially, the macros also reconstruct and execute the command 'wmipr oces cal c reat mshta C:\ProgramData\zihtujs.rtf', which attempts to download and execute a payload from the URL http://157.230.250.107:8080/mfkrmotherfuckeru6y82sasswhorehf9e and save it as 'C:\ProgramData\zihtujs.rtf'. The use of XLM macros and the download-and-execute pattern are indicative of a downloader, but a specific family cannot be confidently identified.

Heuristics 5

  • 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.
  • XLM Auto_Open with dangerous formula APIs critical OLE_XLM_DANGEROUS_FN
    Excel 4.0 macro sheet contains an Auto_Open / Auto_Close entry and dangerous XLM formula APIs that can invoke programs, write files, or transfer control without VBA.
  • URL reconstructed from XLM cell array (4 URLs) critical OLE_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across the BIFF8 Shared String Table (one quoted-char SST entry concatenated with & at runtime) or across individual numeric cells (one ASCII charcode per cell). 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 BIFF8 record stream and decoding SST entries plus LABELSST/RK/NUMBER cells.
  • 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.
  • 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 http://157.230.250.107:8080/mfkrmotherfuckeru6y82sasswhorehf9e
    • https://cdn.discordapp.com/attachments/911246617275957290/915526461379727370/GYRxsMXKtvwSwhoreniggagay.bin
    • https://cdn.discordapp.com/attachments/911246617275957290/915526473467719720/KsXtuXmxoZvgudVwhoreniggagay.bin
    • https://cdn.discordapp.com/attachments/911246617275957290/915526468073848872/xTpcaEZvwmHqwhoreniggagay.bin

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_macros.txt
0d3b5690881ad73db5d9204975150d75497c39f1fccd21aa2dba7fa4cab2cc38		 xlm-macro oletools.olevba.extract_all_macros (XLM macro listing) 212596 bytes

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