Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 9e505e43330b47e8…

MALICIOUS

Office (OLE) / .XLSX

208.4 KB First seen: 2022-05-10
MD5: 6a991d1c54a9eb4dc144bb627cfbff87 SHA-1: 14514edb4620d419a3ad3638c9c7869431ecc806 SHA-256: 9e505e43330b47e89796ff9478c47c614946a189316d463d51b6aa56374f8641
240 Risk Score

Malware Insights

Formbook · confidence 95%

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

The file is a password-encrypted Excel spreadsheet, a common technique to evade static analysis. The presence of an Equation Editor OLE object within the spreadsheet is a critical indicator of malicious intent, often used to exploit vulnerabilities. ClamAV identifies this as Doc.Downloader.Formbook, strongly suggesting it's a Formbook downloader variant. The embedded OLE object is the primary mechanism for delivering the malicious payload.

Heuristics 6

  • 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.
  • 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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