Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 bbb87b1597706721…

MALICIOUS

Office (OLE) / .XLSX

187.6 KB First seen: 2022-04-06
MD5: 29f331431ec4a5d880b8cdc468a7df9b SHA-1: f54ed458a8979ff032096a34a60273a679569d64 SHA-256: bbb87b159770672158d5a50a29451faec20bb7d7209e054fee48f2504b630dc4
280 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1566.001 Spearphishing Attachment T1204.002 Malicious File

The sample is a password-encrypted XLSX file that contains an embedded Equation Editor OLE object. Heuristics indicate this object is anomalous and exploits CVE-2018-0798, a known vulnerability for delivering malicious content. ClamAV detection confirms this as a Formbook downloader. The encryption and exploitation of the Equation Editor suggest the document is designed to bypass initial security checks and execute a secondary payload.

Heuristics 7

  • Equation Editor OLE object high CVE related OLE_EQUATION_EDITOR
    Default-encrypted OOXML 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
    Default-encrypted OOXML contains embedded Equation Editor data with anomalous native stream bytes consistent with a CVE-2018-0798-style exploit. This is treated as likely CVE evidence because the Equation object is malformed and payload-like.
  • Encrypted Office package with CFB FAT corruption critical OLE_ENCRYPTED_AND_MALFORMED
    Encrypted-package shape co-occurs with FAT-chain corruption — the documented combined evasion form.
  • ClamAV: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0
  • Default-encrypted OOXML exploit carrier layout high OOXML_ENCRYPTED_EXPLOIT_CARRIER_SHAPE
    Default-password encrypted OOXML package contains embedded OLE object parts and additional activation/decoy parts. This layout is common in malicious Excel exploit delivery and requires inspecting the decrypted package.
  • Office document is password-encrypted medium OFFICE_ENCRYPTED_PACKAGE
    OLE container holds MS-OFFCRYPTO encrypted package (Standard Encryption (Office 2007, AES)).
  • Office OOXML encrypted with default VelvetSweatshop password medium OFFICE_DEFAULT_PASSWORD_ENCRYPTED_OOXML
    OLE EncryptedPackage decrypts with Excel's built-in VelvetSweatshop password. Office opens this transparently, and malware uses it to hide OOXML exploit parts from scanners that only inspect the outer OLE container.

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