Formbook — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 858d2228753506ee…

MALICIOUS

Office (OOXML) / .XLSX

180.0 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000 First seen: 2022-03-03
MD5: 3cefd5a284edb7483895cb6d4bebd6dd SHA-1: 9025e40488697165da46df2ea6392a71b221d30f SHA-256: 858d2228753506ee1a04c27a0136d8981939826057c291f44fd9085728efd75e
228 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1203 Exploitation for Client Execution T1566.001 Spearphishing Attachment

The file is an Excel document containing an embedded Equation Editor OLE object, which is known to be vulnerable to CVE-2018-0798. ClamAV detections indicate this is a downloader for the Formbook family. The embedded object likely serves as the initial execution vector to download and run a secondary payload.

Heuristics 6

  • 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
  • ClamAV detection on extracted artifact critical EXTRACTED_FILE_CLAMAV
    ClamAV flagged at least one file extracted from inside this sample. Even when the wrapping document carries no AV detection of its own, a hit on the carved artifact is a strong indicator the sample is a delivery vehicle.
  • 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 4

Files carved from inside the sample during analysis.

FilenameKindSourceSize
ooxml_oleobject_00.bin
36241cd584a6c91eb88212889ba0e6b89930d336838ef339d54fd31905c908c8		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject1.bin 3584 bytes
ooxml_oleobject_00_ole10native_00.bin
d26ea91ec79d27cc1ab1ac58ea504f53b55f0feb93562c27cdef4e2705774a57		 ole-package OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OLe10NatIvE 1401 bytes
ooxml_oleobject_01.bin
9ac2b97869597f4ee47908cd979006916374793a058f212d481bf78a3c9069b5		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/Microsoft_Office_Word_Macro-Enabled_Document1.docm 59370 bytes
Detection
ClamAV: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0
Obfuscation or payload: unlikely
emf_00.emf
bc1a75f99b79c98350da4bb5561eac01186dacf8d64f3ae8d4822e1a028644d9		 ooxml-emf OOXML EMF part: xl/media/image7.emf 1099960 bytes

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