Formbook — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 cf2ad77f187c894b…

MALICIOUS

Office (OOXML) / .XLSX

180.4 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000
MD5: 39a5ba533e4bdbc05193d292ed1794c9 SHA-1: 5ec29e0b37ec4d724d211e2745d40fc6dfeb1308 SHA-256: cf2ad77f187c894b75762d8d4dda3a02d3483ee99b2a3078348308b2a476d902
168 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1204 Malicious File T1204.002 Malicious File: Malicious Attachment T1059 Command and Scripting Interpreter

The critical ClamAV detection identifies this file as Doc.Downloader.Formbook, a known downloader. The presence of an embedded Equation Editor OLE object, coupled with heuristics indicating CVE-2018-0798, strongly suggests exploitation of a vulnerability within the Equation Editor to facilitate the download and execution of a secondary payload. The hidden worksheet is a common tactic to conceal malicious content.

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
a74046b1cc766295613cdd0e171cf5b09578f8d6f360dab69bb91ab9f3c00eb6		 ooxml-ole-object OOXML embedded OLE part: xl/embeddings/oleObject1.bin 3584 bytes
ooxml_oleobject_00_ole10native_00.bin
8e4e26f7e922af0505dfc42f67c7063852a7e813c724e48133b59dc224881209		 ole-package OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OlE10NaTIve 1275 bytes
emf_00.emf
874888f7f81ec7ad000d79f455d4bc55716d54c177cca0732abeda7641b486bf		 ooxml-emf OOXML EMF part: xl/media/image7.emf 1099960 bytes

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