Formbook — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 4209335df402c33e…

MALICIOUS

Office (OOXML) / .XLSX

179.6 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000 First seen: 2022-03-02
MD5: 42af37945df020c89e9cab150dbeefc4 SHA-1: c861ea0a9177aa1fb34c69a08f4f579176f7032e SHA-256: 4209335df402c33ee8e988161ad26801382db9d0ccd9e302fc8db9ed0164056e
168 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1204 Malicious Link T1204.001 Malicious Link: Malicious Link T1566 Phishing T1566.001 Phishing: Spearphishing Attachment T1059 Command and Scripting Interpreter

The critical ClamAV detection explicitly identifies the sample as 'Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0', indicating it is a Formbook downloader. High-severity heuristics confirm the presence of an Equation Editor OLE object with anomalies consistent with CVE-2018-0798, a known vulnerability exploited for initial payload delivery. The hidden worksheet heuristic suggests an attempt to conceal malicious content. The overall attack pattern involves exploiting this vulnerability 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
3e66e4e6ebe6204a05f81d1a47d1f2ab54147c253a8990f77a841f3833005792		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject1.bin 4096 bytes
ooxml_oleobject_00_ole10native_00.bin
409793e86770c777a1089b1b7f5b3ae39a533bd6daac3ecaa01b4d500cec4569		 ole-package OOXML xl/embeddings/oleObject1.bin Ole10Native stream: olE10NaTIvE 1592 bytes
emf_00.emf
bc1a75f99b79c98350da4bb5561eac01186dacf8d64f3ae8d4822e1a028644d9		 ooxml-emf OOXML EMF part: xl/media/image7.emf 1099960 bytes

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