Blocking network access based on endpoints

You can use endpoint IP filtering to block traffic from source IP addresses associated with endpoints. You can also configure FortiOS Carrier to record log messages whenever endpoint IP filtering blocks traffic. Endpoint IP filtering blocks traffic at the IP level, before the traffic is accepted by a security policy.

To configure endpoint IP filtering, go to Security Profiles > Carrier > IP Filter and add endpoints to the IP filter list. For each endpoint you can enable or disable both blocking traffic and logging blocked traffic.

FortiOS Carrier looks in the current user context list for the endpoints in the IP filter list and extracts the source IP addresses for these endpoints. Then any communication session with a source IP address that matches one of these IP addresses is blocked at the IP level, before the communication session is accepted by a security policy.

FortiOS Carrier dynamically updates the list of IP addresses to block as the user context list changes. Only these updated IP addresses are blocked by endpoint IP filtering.

For information about the carrier endpoints and the user context list, including how entries are added to and removed from this list.

MMS Content Checksum

The MMS content checksum feature attempts to match checksums of known malicious MMS messages, and on a successful match it will be blocked. The checksums are applied to each part of the message—attached files and message body have separate checksums. These checksums are created with CRC-32, the same method as FortiAnalyzer checksums.

For example, if an MMS message contains a browser exploit in the message body, you can add the checksum for that message body to the list, and future occurrences of that exact message will be blocked. Content will be replaced by the content checksum block notification replacement message for that type of MMS message, and if it is enabled the event will be logged.

One possible implementation would to configure all .sis files to be intercepted. When one is found to be infected or malicious it would be added to the MMS content checksum list.

To use this feature a list of one or more malicious checksums must be created and then the feature is enabled using that list. For a detailed list of options, see MMS Content Checksum.

To configure an MMS content checksum list

1. Go to Security Profiles > MMS Content Checksum.
2. Select Create New.
3. Enter a name for the list of checksums, and select OK. You are taken to the edit screen for that new list.
4. Select Create New to add a checksum.
5. Enter the Name and Checksum, and select OK. The checksum is added to the list.

To add more checksums to the list, repeat steps 4 and 5.

To to remove a checksum from the list you can either delete the checksum or simply disable it and leave it in the list.

To enable MMS content checksums, expand MMS Scanning and select MMS Content Checksum for the selected MMS types. Select the checksum list to match.

Passing or blocking fragmented messages

Select to pass fragmented MM3 and MM4 messages. Fragmented MMS messages cannot be scanned for viruses. If you do not select these options, fragmented MM3 and MM4 message are blocked.

The Interval is the time in seconds before client comforting starts after the download has begun, and the time between sending subsequent data.

The Amount is the number of bytes sent by client or server comforting at each interval.

Client comforting

In general, client comforting is available for for MM1 and MM7 messaging and provides a visual display of progress for web page loading or HTTP or FTP file downloads. Client comforting does this by sending the first few packets of the file or web page being downloaded to the client at configured time intervals so that the client is not aware that the download has been delayed. The client is the web browser or FTP client. Without client comforting, clients and their users have no indication that the download has started until the Carrier-enabled FortiGate unit has completely buffered and scanned the download. During this delay users may cancel or repeatedly retry the transfer, thinking it has failed.

The appearance of a client comforting message (for example, a progress bar) is client-dependent. In some instances, there will be no visual client comforting cue.

During client comforting, if the file being downloaded is found to be infected, then the Carrier-enabled FortiGate unit caches the URL and drops the connection. The client does not receive any notification of what happened because the download to the client had already started. Instead the download stops, and the user is left with a partially downloaded file.

If the user tries to download the same file again within a short period of time, then the cached URL is matched and the download is blocked. The client receives the Infection cache message replacement message as a notification that the download has been blocked. The number of URLs in the cache is limited by the size of the cache.

Client comforting can send unscanned (and therefore potentially infected) content to the client. Only enable client comforting if you are prepared to accept this risk. Keeping the client comforting interval high and the amount low will reduce the amount of potentially infected data that is downloaded.