Proxy mode stream-based scanning

Stream-based scanning provides the following AV improvements over legacy scan mode:

  • Archive files (ZIP, GZIP, BZIP2, TAR, ISO) that exceed the oversize limit are uncompressed and scanned for infections.

  • The contents of large archive files are scanned without having to buffer the entire file.
  • Small files are scanned locally by the WAD daemon if only AV scanning is needed in the policy.
  • File filtering on HTTP/HTTPS is handled locally by the WAD daemon.

This means that the overall memory usage is optimized when an archive file is scanned, and better security is achieved by scanning archives that would otherwise be bypassed.

However, stream-based scanning has limitations on the more complex features that it can scan. For the following features, traffic will be automatically handed off to the scanunit daemon for scanning (as in the case of legacy mode):

  • Heuristic AV scan
  • DLP
  • Quarantine
  • FortiGuard outbreak prevention and external block list
  • Content disarm
To configure the scan mode:
config antivirus profile
    edit <name>
        set feature-set proxy 
        set scan-mode {default | legacy}

TCP windows

Some file transfer applications can negotiate large TCP windows. For example, WinSCP can negotiate an initial TCP window size of about 2GB.

The TCP window options can be used to prevent overly large initial TCP window sizes, helping avoid channel flow control issues. It allows stream‑based scan's flow control to limit peers from sending data that exceeds a policy's configure