Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 f5db91253eb9e54e…

MALICIOUS

Office (OLE) / .XLSX

187.7 KB First seen: 2022-04-06
MD5: 4edd9483d5964b6e31c9c50e422e2654 SHA-1: 52da967333dd510e448c311853bb2f6475892d71 SHA-256: f5db91253eb9e54e31769c60b8ef34d248e0f07008eab10f3cab493c823818fb
240 Risk Score

Malware Insights

Formbook · confidence 95%

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

The file is a password-encrypted Office document, identified as a malicious downloader by ClamAV and associated with the Formbook family. The presence of an Equation Editor OLE object within the encrypted package is a strong indicator of exploit delivery. This object is known to be used to execute arbitrary code, likely to download and run 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.