Formbook Office (OOXML) / .XLSX malware analysis — malicious · b34c09bf9e0459b2

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 8323328ee54a8d0afd9e421a556a57b7 SHA-1: 836ff26907fc87551205ccf178b1f4bc7a3486df SHA-256: b34c09bf9e0459b2a09c73eb3f1c43d87861c64bbbbe26e59bfc243ef589f720

210 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK

T1204 Malicious File Execution T1059 Command and Scripting Interpreter

The sample contains an embedded Equation Editor OLE object that exhibits anomalies consistent with CVE-2018-0798. ClamAV identifies the file as Doc.Downloader.Formbook, indicating it functions as a downloader for the Formbook malware family. The presence of a hidden worksheet further suggests an attempt to conceal malicious content.

Heuristics 7

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
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` `c4e63cce5d87c59fde5a5019f950c70ac587697fe32c1464d4bad064560bbfde`	ooxml-ole-object	OOXML embedded OLE part: xl/embeddings/oleObject1.bin	1454592 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact entropy is 7.99, consistent with packed or encrypted content.
`ooxml_oleobject_00_ole10native_00.bin` `262651227f95c5342b57cdf1eab88abb29296f8a40871ab57ba129bce56426c0`	ole-package	OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OLe10nAtivE	1440302 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` `a06f4e5b0dcbf6e6a1bf08cf2b8993fd1109c7e2552e23fe79ad14767716ee90`	ooxml-emf	OOXML EMF part: xl/media/image2.emf	1099960 bytes

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