Formbook — PDF malware analysis

Static analysis result for SHA-256 99abee8804404753…

MALICIOUS

PDF

184.0 KB
MD5: 7a432f2345a0adde185ce077da235f1e SHA-1: 48458f51520db98616536ef548373e5b0e325d61 SHA-256: 99abee880440475305d2033cacd0924796f3ea2eabc3092c6d01d71fe85359f7
178 Risk Score

Malware Insights

Formbook · confidence 85%

MITRE ATT&CK
T1204.002 User Execution: Malicious File T1027 Obfuscated Files or Information T1129 Shared Infrastructure

The sample is a PDF containing an embedded binary artifact (embedded_file_obj0022.bin) and JavaScript. ClamAV has explicitly flagged both the PDF and the extracted binary as Doc.Downloader.Formbook, providing high confidence in the family attribution. The document body consists of an image-only lure to trick the user into executing the payload.

Machine Learning

  • Nyx PDF Classifier malicious score 0.9384

Heuristics 7

  • ClamAV: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0
  • ClamAV detection on extracted artifact critical EXTRACTED_FILE_CLAMAV
    ClamAV flagged at least one file extracted from inside this sample. Even when the wrapping document carries no AV detection of its own, a hit on the carved artifact is a strong indicator the sample is a delivery vehicle.
  • Embedded file low PDF_EMBEDDED
    PDF embeds a file attachment — could carry an executable or another weaponised document as a nested payload
  • JavaScript action low PDF_JAVASCRIPT
    PDF contains a /JavaScript action. Generic JavaScript is common in benign forms; specific dangerous APIs are scored by separate rules. (matched inside decoded stream)
  • Embedded JS stream low PDF_JS
    PDF references a /JS stream. Generic JavaScript is common in benign forms; specific dangerous APIs are scored by separate rules. (matched inside decoded stream)
  • PDF paints image(s) but contains no text operators info PDF_IMAGE_ONLY_LURE
    PDF has 1 image XObject(s) and the content stream contains no text-emitting operators (BT/ET, Tj, TJ, ', ") in either raw bytes or decompressed streams — this is the screenshot-as-PDF pattern used to bypass text-based scanners and to deliver instructions purely through rendered pixels. It is informational unless paired with invisible links or risky URI context.
  • Suspicious extracted artifact info EXTRACTED_FILE_STATIC_TRIAGE
    One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
embedded_file_obj0022.bin
9c2dea0d4a3aff05238354847405e7846092a989799c4130ec98736ddad1a44b		 pdf-embedded-file PDF EmbeddedFile object 22 at offset 0x1B51 187176 bytes
Detection
ClamAV: Doc.Downloader.Formbook-bc97c1e0c33c3c93-9951465-0
Obfuscation or payload: likely
Carved artifact entropy is 7.96, consistent with packed or encrypted content.
stream_004_off0002dc95.bin
cb93b4a1e0ac3266fc587a202ff3b0e475cad633393f80b126ebd97de5649005		 decompressed-pdf-stream PDF FlateDecoded stream at offset 0x2DC95 846 bytes

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