Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 f99bacd156ae3b18…

MALICIOUS

Office (OLE) / .XLSX

187.3 KB
MD5: bdec29d2bcc58b0de11381847304c76e SHA-1: cec0472eaa37d22e7a290c44127e135bc053db85 SHA-256: f99bacd156ae3b183520421d51111123cab9c867506892d9a999b8aa3bf8f6de
280 Risk Score

Malware Insights

Formbook · confidence 90%

MITRE ATT&CK
T1203 Exploitation for Client Execution T1027 Obfuscated Files or Information T1566.001 Phishing: Spearphishing Attachment T1204.002 User Execution: Malicious File T1204.001 User Execution: Malicious Link T1027.001 // a bit too many, let's refine it to the most relevant ones T1203 Exploitation for Client Execution T1203 Exploitation for Client Execution

The sample is a password-encrypted Office document that uses the default 'VelvetSweatshop' password to bypass security controls. It contains an embedded OLE object (xl/embeddings/oleObject1.bin) that triggers CVE-2018-0798 in the Equation Editor to execute code. ClamAV detection specifically identifies this as a Formbook downloader.

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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