Formbook Office (OOXML) / .XLSX malware analysis — malicious · 79b3390ca3d58a94

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: c31ef8e8050559e76416f973be8c1693 SHA-1: c7ab3fc18325ea523c341e938883709963799f2c SHA-256: 79b3390ca3d58a94ae3787cb70a2de2365981380d2f92bd6b554ae578455f157

210 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK

T1204 Malicious File T1204.002 Malicious File: User Execution: Malicious Attachment T1059 Command and Scripting Interpreter T1566 Phishing T1566.001 Phishing: Spearphishing Attachment

The file is an Excel document containing an embedded OLE object, specifically exploiting CVE-2018-0798 in the Equation Editor. This vulnerability is known to be used for downloading and executing secondary payloads. ClamAV detection confirms this as a Formbook downloader. The presence of a high-entropy Ole10Native stream within the Equation Editor object strongly suggests it contains malicious code intended for execution.

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` `dd224401d4c9eaf0aacb979881bde033abbc5170007de4f7bf424eb013106521`	ooxml-ole-object	OOXML embedded OLE part: xl/embeddings/oleObject1.bin	2149888 bytes
Detection ClamAV: No threats found Obfuscation or payload: likely Carved artifact entropy is 7.98, consistent with packed or encrypted content.
`ooxml_oleobject_00_ole10native_00.bin` `a792661dc12858a66f116f7418e3fc3d8e07e2fa7decd43cd5fe35d402b05d10`	ole-package	OOXML xl/embeddings/oleObject1.bin Ole10Native stream: oLE10natIve	2130738 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` `e4a1a99c5fdcb7b2c808297861e06daa5e8fd10c94eacb5d8a1060c9a9e26122`	ooxml-emf	OOXML EMF part: xl/media/image2.emf	1099960 bytes

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