Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 4a616828c64cce04…

MALICIOUS

Office (OLE) / .XLSX

208.4 KB First seen: 2022-05-10
MD5: be79cafcbbab25a5b17a369212053180 SHA-1: d680869fe3adf7ef57ace7515a4b5dffe6b31bdd SHA-256: 4a616828c64cce0475ca1a8867985730f19b64e896ae029ce41582eaebf65320
280 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1204.002 Malicious File: User Execution of Malicious Code T1559.001 Component Object Model Hijacking

The sample is a password-encrypted Office document containing an embedded Equation Editor OLE object, which is a known exploit carrier. High-severity heuristics indicate the exploitation of CVE-2018-0798 via anomalous Equation Editor native stream data. ClamAV detection explicitly names this as 'Doc.Downloader.Formbook', confirming the family and its role as a downloader. The document's encrypted nature and the exploit carrier strongly suggest it's designed to trick the user into opening it and triggering the exploit, leading to the download of further malicious content.

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.