Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 f40444c84167df36…

MALICIOUS

Office (OLE) / .XLSX

187.7 KB First seen: 2022-04-04
MD5: 12a10de86c7650fc4e6dadbc081e0dd0 SHA-1: 5da728348569fcc7defbd7e46b789ee3483efb49 SHA-256: f40444c84167df3670bb9f31f45b23dc9d5f94c4d0ad991e3a2f7cb27c8275dd
280 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1204 Malicious Link T1566 Phishing

The sample is a password-encrypted OOXML file identified as a malicious downloader by ClamAV. High-severity heuristics indicate the presence of an Equation Editor OLE object, specifically triggering CVE-2018-0798, which is a known exploit carrier. The file is also flagged for malformed structure and encryption, consistent with exploit delivery mechanisms. The ClamAV detection name 'Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0' strongly suggests the Formbook family.

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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