Antivirus introduction
FortiOS offers antivirus solutions in two modes: flow-based and proxy-based. Users can select the mode that best suits their needs. The default setting for a new antivirus profile is flow-based inspection, which is generally recommended unless there is a need for features specific to proxy. For more information, see Protocol comparison between antivirus inspection modes.
FortiOS includes two preloaded antivirus profiles:
- default
- wifi-default
You can customize these profiles, or you can create your own to inspect certain protocols, remove viruses, analyze suspicious files with FortiSandbox, and apply botnet protection to network traffic. Once configured, you can add the antivirus profile to a firewall policy.
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This functionality requires a subscription to FortiGuard Antivirus. |
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In order to download updated AV definitions, at least 1 policy with a security profile that has Antivirus scanning must be enabled. |
Protocol comparison between antivirus inspection modes
The following table indicates which protocols can be inspected by the designated antivirus scan modes.
|
|
HTTP |
FTP |
IMAP |
POP3 |
SMTP |
NNTP |
MAPI |
CIFS |
SSH |
|---|---|---|---|---|---|---|---|---|---|
|
Proxy |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes* |
Yes |
|
Flow |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
No |
Yes |
No |
* Proxy mode antivirus inspection on CIFS protocol has the following limitations:
- Cannot detect infections within some archive files.
- Cannot detect oversized files.
Other antivirus differences between inspection modes
Starting from 6.4.0, the scan mode option is no longer available for flow-based AV.
This means that AV no longer exclusively uses the default or legacy scan modes when handling traffic on flow-based firewall policies. Instead, AV in flow-based policies uses a hybrid of the two scan modes. Flow AV may use a pre-filtering database for malware detection in some circumstances as opposed to the full AV signature database in others. The scan method is determined by the IPS engine algorithm that is based on the type of file being scanned. When handling oversized files in flow-based AV, the action can either be pass (default) or block. When the action is pass, IPS appends to-be-scan data into the AV scan buffer. If the appended file size exceeds the oversize-limit that is defined in the protocol option profile, then the AV session is cleared and the file is bypassed from AV scanning.
In contrast, proxy mode maintains the scan mode option, which can be toggled between default or legacy mode. In default mode, the WAD daemon receives the file and then decides if it can do an in-process scan of the file in simple AV configuration scenarios. If the file is in an oversized archive that is supported by the stream‑based decompressor, then it is sent to stream‑based scan for best effort inspection. Stream‑based scan decompresses and scans the entire archive without archiving the file. If the file is not supported by stream‑based scan, then it is buffered and then sent to the scanunit daemon for inspection on content that is under the oversize limit.
In legacy mode, stream-based scanning is disabled, so oversized archive files and files that cannot be handled by WAD in-process scan are buffered and sent to the scanunit daemon for processing.