Formbook Office (OOXML) / .XLSX malware analysis — malicious · b60353ac3859a0ca

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 736e0aa496783aa3904286c5e553477c SHA-1: 16fed8fb7046086b54f091eb8af1e4ffa70fefb1 SHA-256: b60353ac3859a0ca911479c2b8542d77e3d9bc413a77ca07093e50d7a4398a2a

210 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK

T1204 Malicious Link T1204.002 Malicious File T1566 Phishing T1566.002 Spearphishing Attachment

The sample is an Excel file containing an embedded OLE object, specifically a Microsoft Equation Editor object. Heuristics indicate this object exploits CVE-2018-0798, a vulnerability associated with the Equation Editor. ClamAV detection identifies the file as Doc.Downloader.Formbook, suggesting it acts as a downloader for the Formbook malware family. The embedded object likely contains and executes the malicious payload.

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` `932e0b32899b6d0b9d57f95206dbe31b3224670a6d93241e2b2cb4a2cc1faf08`	ooxml-ole-object	OOXML embedded OLE part: xl/embeddings/oleObject1.bin	2028032 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` `90ab3b1298200f2ba4b4e3b57b6632f047c6c428293ef2cee9922ce98bc820f6`	ole-package	OOXML xl/embeddings/oleObject1.bin Ole10Native stream: OlE10NaTivE	2009698 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` `86fcb1a75a1d7657a7d3bed827557074695799a7d08da26aa50565e7fef95edd`	ooxml-emf	OOXML EMF part: xl/media/image2.emf	1099960 bytes

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