Formbook Office (OOXML) / .XLSX malware analysis — malicious · 7689fde52d772a68

MALICIOUS

Office (OOXML) / .XLSX

2.47 MB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 12.0000

MD5: dc677a3b50b7659c944615f6e04ea29d SHA-1: 36a7e78bd13be55a1c62b73203e80c6f61c45eab SHA-256: 7689fde52d772a6810cccf89d32a6bb8e944a9ce435a44dc52032feeee61d6eb

250 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK

T1204 Malicious File Execution T1059 Command and Scripting Interpreter

The sample is an Excel file containing an embedded OLE object, specifically an Equation Editor object. Heuristics indicate this object exploits CVE-2018-0798, a vulnerability in Equation Editor, and carries a payload within its native stream. ClamAV detection confirms this as a Formbook downloader, which is known to exploit such vulnerabilities to fetch and execute further malicious content.

Heuristics 8

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
x86 GetPC stub (CALL $+5; POP ESI) high SC_GETPC_CALL

x86 GetPC stub (CALL $+5; POP ESI)
Equation Editor object carries payload-like Ole10Native stream high OLE_EQUATION_OLE10NATIVE_PAYLOAD_ANOMALY

Embedded OLE object declares the Equation Editor CLSID but stores a large high-entropy Ole10Native stream with malformed package sizing. This is an exploit-shaped Equation/OLE payload container seen in malicious OOXML samples. It is not assigned to a specific CVE unless the MTEF/Equation Native primitive also matches.
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
Suspicious extracted artifact info EXTRACTED_FILE_STATIC_TRIAGE

One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.

Extracted artifacts 3

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`ooxml_oleobject_00.bin` `a958431bab50b4729ba6cb885b23ef03b17be1ba3305e88b136977ef9b77401b`	ooxml-ole-object	OOXML embedded OLE part: xl/embeddings/oleObject1.bin	2411008 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact entropy is 7.97, consistent with packed or encrypted content.
`ooxml_oleobject_00_ole10native_00.bin` `18eae7e21512bfd83a7d460891413342586aa5c0180930761d1c2c3a338675e3`	ole-package	OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OLE10NATiVe	2390000 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact entropy is 7.99, consistent with packed or encrypted content.
`emf_00.emf` `3ec09f9d4895d47bbb941d14ee4b9bde7530b4aa97ae5c1eb5398e9bf7e4cd51`	ooxml-emf	OOXML EMF part: xl/media/image2.emf	1099960 bytes

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