Formbook — Office (OLE) / .XLSX malware analysis

Static analysis result for SHA-256 2c25348cfc00877a…

MALICIOUS

Office (OLE) / .XLSX

187.6 KB First seen: 2022-02-17
MD5: a2f5e30d5c608d7624d9753dad99f65b SHA-1: c48d56b9785b0f69296b097c24bb1d7c32c054df SHA-256: 2c25348cfc00877a79e71c448f13c0ff1bf7a76ca6a0eee7e2f64b43420ead64
240 Risk Score

Malware Insights

Formbook · confidence 95%

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

The sample is a password-encrypted Office document, identified by ClamAV as Doc.Downloader.Formbook. The presence of an Equation Editor OLE object within the encrypted OOXML structure strongly suggests it's designed as an exploit carrier. The encryption and malformed structure indicate an attempt to evade static analysis and deliver a secondary payload, consistent with Formbook downloader behavior.

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.