Formbook — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 f8232215f9c11f61…

MALICIOUS

Office (OOXML) / .XLSX

180.8 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000
MD5: f91d93f810f4605b2326cd3d6f53ef2f SHA-1: 55da94e62cbd510d50f6a5d19599990649c37025 SHA-256: f8232215f9c11f6163d5ac70cd07b97ffb05a26d0554f728de38c30815ae4815
168 Risk Score

Malware Insights

Formbook · confidence 95%

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

The critical ClamAV heuristic identifies the file as 'Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0', strongly suggesting the Formbook family. High-severity heuristics indicate the presence of an Equation Editor OLE object, specifically exploiting CVE-2018-0798, which is a common delivery mechanism for malware like Formbook. This object likely serves to download and execute a secondary payload.

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
24ec9765ebcef089fe6eb8d7e392c9f6c9461193e6130c841a48f791c6764046		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject1.bin 4096 bytes
ooxml_oleobject_00_ole10native_00.bin
951d5b255da66fe21c87fc158167c4e6f273c5260b99d60bd71ef82873e6c2cf		 ole-package OOXML xl/embeddings/oleObject1.bin Ole10Native stream: oLe10NativE 1525 bytes
emf_00.emf
fb561e7b6f0b4bfdbf1d1371da92150b2859718e7e4017cbe4cb36148c57cf40		 ooxml-emf OOXML EMF part: xl/media/image7.emf 1099960 bytes

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