Formbook — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 39b183293cf97134…

MALICIOUS

Office (OOXML) / .XLSX

180.7 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000
MD5: 24288083f44d7919bb85eb80f477161b SHA-1: 7e6f6bcbc8af4a9894a0137947575929ce9e3550 SHA-256: 39b183293cf97134d5e408ddf4f50a479e5c1252377148b6cb7c8aef6926661e
168 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1204.002 Malicious File T1566.001 Spearphishing Attachment

The file is an Office document containing an embedded OLE object, specifically identified as an Equation Editor object. High-severity heuristics indicate a vulnerability exploitation related to CVE-2018-0798 within this object. ClamAV detection explicitly names the file as 'Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0', strongly suggesting the Formbook family and a downloader functionality. The presence of hidden sheets further supports the likelihood of malicious code concealment.

Heuristics 5

  • Equation Editor OLE object high CVE related OLE_EQUATION_EDITOR
    Embedded OLE object xl/embeddings/oleObject1.bin contains the Equation Editor CLSID, the legacy component exploited by CVE-2017-11882, CVE-2018-0802, and CVE-2018-0798.
  • CVE-2018-0798 — anomalous Equation Editor native stream high CVE likely CVE_2018_0798_EQUATION_NATIVE_ANOMALY
    Embedded Equation Editor OLE data contains anomalous native stream bytes consistent with a CVE-2018-0798-style Equation Editor exploit. This is treated as likely CVE evidence because the Equation object is malformed and payload-like, but it does not match the exact public matrix-overflow byte signature.
  • ClamAV: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0
  • Embedded OLE object medium OOXML_OLE_OBJECT
    Document contains an embedded OLE object
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 1 hidden sheet(s) — hidden sheets are commonly used to conceal macro code, staging data, or intermediate payload construction

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
ooxml_oleobject_00.bin
bdfdfd47b3753d939bf0591658147e634b94bf2fccb2403cc3bac27aa63ea5c8		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject1.bin 3584 bytes
ooxml_oleobject_00_ole10native_00.bin
033b57d88045d0dc9baf15e1ffc6c9f0ef9d41e8481e6d735309d0531739cc6c		 ole-package OOXML xl/embeddings/oleObject1.bin Ole10Native stream: ole10NaTiVE 1360 bytes
emf_00.emf
ed3c07104197ca14cf79cca8a46789c37f947caf674ce94c9622ab652a135aac		 ooxml-emf OOXML EMF part: xl/media/image7.emf 1099960 bytes

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