Formbook Office (OOXML) / .XLSX malware analysis — malicious · e55fec1d49a6d680

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: ee2ea2a9f7d621c21b157f6328ed4966 SHA-1: 0fec024ff1171fccf22092df1630ff80d4d181f9 SHA-256: e55fec1d49a6d6809fd10fabbdfc395dac4fad9f0f42ad486a1147ad7aaa910a

210 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK

T1204 Malicious Link T1204.002 Malicious File T1059 Command and Scripting Interpreter

The sample is an Excel file containing an embedded Equation Editor OLE object, which is known to be vulnerable to CVE-2018-0798. The high entropy and anomalous native stream within the Equation Editor object strongly suggest it carries a malicious payload. ClamAV detection confirms this, identifying it as Doc.Downloader.Formbook, indicating the likely intent is to download and execute a secondary stage malware. No scripts were extracted, but the embedded OLE object is sufficient evidence of malicious intent.

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` `a3c68ae4f0279fb10d1246a2730129874720dcd548a6809a49bd00a3f618c9f2`	ooxml-ole-object	OOXML embedded OLE part: xl/embeddings/oleObject1.bin	1931264 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` `29b73e09730373a103c4ba80f718aae426f088cfa7eb3a2a12be292dfb505a6e`	ole-package	OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OLe10NatIVe	1913585 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` `f45233de7e01ce7e72f762a2f792fb13ea5db58c2aa8ad8d291d1052bb7e8138`	ooxml-emf	OOXML EMF part: xl/media/image2.emf	1099960 bytes

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