Definition
Identifying and extracting files from network application protocols through the use of network stream reassembly software.
How it works
Protocol stream reassembly software recreates a directional byte stream by analyzing captured network packets. Once the stream is reassembled pattern matching is applied to determine if it contains a file of interest. Files of interest range from executable, archive, or document file formats. Once the file is captured, it is then processed with standard File Analysis Techniques. Example network protocols include HTTP, SMTP, FTP, HTTP/2, and TLS/HTTP/Dropbox.
Considerations
- This is an error prone process due to the intricacies of network protocols and network packet capture. For example reassembly may be done in real-time or streaming fashion, or packets may be written to disk, then bulk processed. The packets may arrive out of order, with fragmentation, duplicates, or re-transmissions. The reassembly software must compensate for the imperfect packet stream in order to recreate the well formed file which was transmitted.
- File type identification can be a difficult process which can be exploited by adversaries.
Implementation perspective
File Carving should be treated as a technical defensive capability rather than a product checkbox. In practice, teams should define the protected scope, the conditions under which the technique acts, and the observable evidence that demonstrates the intended behavior. For this technique, likely engineering context includes File Transfer Network Traffic.
Use the technique to identify suspicious, unauthorized, or abnormal activity through observable evidence and repeatable analysis.
Questions to ask
- Which events, states, or artifacts must be observed for the analysis to work?
- What analytic logic, threshold, comparison, or signature turns observations into a finding?
- How are expected false positives, blind spots, and environmental variations documented?
- Who receives the result, and what action is expected when the technique produces a finding?
Evidence and validation
- Telemetry and data-source configuration records
- Analytic logic, thresholds, signatures, and version history
- Test cases demonstrating expected positive and negative results
- Alert, triage, escalation, and tuning records
Common failure patterns
- Required telemetry is missing, delayed, or transformed in a way that invalidates the analysis.
- The technique produces alerts without an accountable triage and response process.
- Detection coverage is claimed from product deployment without testing the relevant analytic behavior.
This implementation perspective is original Bare Metal Cyber educational content. It does not replace the official D3FEND definition or establish that a specific product implements the technique.
Technique hierarchy
Top-level family
Parent techniques
Direct child techniques
None listed at this level.
Artifacts and ontology entities
These relationships describe how D3FEND connects a defensive technique to artifacts or other ontology entities. They describe graph semantics, not a product certification.
Explicit technique relationships
Show inferred artifact relationship paths (1)
Offensive-technique relationships
These relationships are generated from D3FEND graph paths and are explicitly experimental. They should be treated as hypotheses for defensive analysis—not as proof that the technique prevents, detects, or removes an offensive behavior.
Authoritative sources
- Open this technique on the official D3FEND website ↗
- Open the official ontology resources ↗
- Computer Worm Defense System and Method ↗FireEye Inc · Ashar Aziz · PatentReference
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