Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 f62dd3bc2bb5fd06…

MALICIOUS

Office (OLE) / .XLSX

186.2 KB First seen: 2022-02-26
MD5: 08f2ec7e8baa306729f4d4a92245ac62 SHA-1: a8f7639191b6865dbc1df731bfcc67a70cba7d9d SHA-256: f62dd3bc2bb5fd06215883de18936590738ca67a7209efca0ea095749ec4b4df
240 Risk Score

Malware Insights

Formbook · confidence 95%

MITRE ATT&CK
T1566.001 Phishing: Spearphishing Attachment T1204.002 Malicious File Execution: Malicious Code

The file is an encrypted Office document, a common delivery mechanism for malicious payloads. The presence of an Equation Editor OLE object and ClamAV detection as 'Doc.Downloader.Formbook' strongly suggests it's a Formbook variant. The encryption and malformed structure indicate an attempt to evade static analysis and likely exploit vulnerabilities upon opening, leading to the download of a second-stage 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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