Duplicate message protection
The convenience offered by MM1 and MM4 messaging can be abused by users sending spam or other unwanted messages. Often, the same message will be sent by multiple subscribers. The message can be spam, viral marketing, or worm-generated messages. MMS duplicate prevention can help prevent this type of abuse by keeping track of the messages being sent.
Overview
Using message fingerprints to identify duplicate messages
Messages from any sender to any recipient
Setting duplicate message thresholds
Duplicate message actions
Notifying duplicate message senders and receivers
Viewing DLP archived messages
Order of operations: flood checking before duplicate checking
Bypassing duplicate message detection based on user’s carrier endpoints
Configuring duplicate message detection
Sending administrator alert notifications
Overview
Duplicate message protection for MM1 messages prevents multiple subscribers from sending duplicate messages to your MMSC. Duplicate message protection for MM4 messages prevents another service provider from sending duplicate messages from the same subscriber to your MMSC. This can help prevent a potential flood that would otherwise become widespread between carriers.
Overview
MM1 and MM4 duplicate message protection
The FortiOS Carrier unit keeps track of the sent messages. If the same message appears more often than the threshold value you configure, then action is taken. Possible actions are logging the duplicates, blocking or intercepting duplicate messages, archiving the duplicate messages, and sending an alert to inform an administrator that duplicates are occurring.
With this highly configurable system, you can prevent the transmission of duplicate messages when there are more than you determine is acceptable.
For detailed configuration options, see Duplicate Message.
Using message fingerprints to identify duplicate messages
Using message fingerprints to identify duplicate messages
The Carrier-enabled FortiGate unit detects duplicates by keeping a record of all the messages travelling on the network and comparing new messages to those that have already been sent.
Rather than save the messages, the FortiOS carrier creates a checksum using the message body and subject. This serves as a fingerprint to identify the message. If another message with the same message body and subject appears, the fingerprint will also be the same and the Carrier-enabled FortiGate unit will recognize it as a duplicate.
By creating and saving message fingerprints instead of saving the messages, the Carrier-enabled FortiGate unit can save resources and time.
Messages from any sender to any recipient
Duplicate message detection will detect duplicate messages regardless of the sender or recipient. To do this, message fingerprints are generated using only the message body and subject. The sender, recipient, and other header information is not included.
If multiple messages appear with the same subject and message body, the Carrier-enabled FortiGate unit will recognize them as being the same.
Setting duplicate message thresholds
The FortiOS Carrier recognizes all duplicate messages, but it will take action when it detects a volume of duplicate messages that exceed the duplicate threshold you set. The threshold defines the maximum number of duplicate messages allowed, the period during which the messages are considered, and the length of time the duplicate message can not be sent by anyone.
For example, you may determine that once a duplicate message is sent more than 300 times in an hour, any attempt to send the same duplicate message will be blocked for 30 minutes.
If a particular duplicate message exceeds the duplicate message threshold and is blocked, any further attempts to send the same message will re-start the block period.
Using the example above, if the duplicate message count exceeds the duplicate threshold, any attempt to send a copy of the duplicate message will be blocked for 30 minutes. If a subscriber tries to send a copy of the message after waiting 15 minutes, the message will be blocked and the block period will be reset to 30 minutes. The block period must expire with no attempts to send a duplicate message. Only then will a subscriber be allowed to send the message. Non-duplicate messages will not reset the block period.
Duplicate message actions
When the Carrier-enabled FortiGate unit detects that a duplicate message has exceeded duplicate threshold, it can take any combination of the five actions you configure for the duplicate threshold.
Notifying duplicate message senders and receivers
| Action | Description | |
| Log | Add a log entry indicating that a duplicate message event has occurred. You must also enable logging for MMS Scanning > Bulk Messages in the Logging section of the MMS protection profile. | |
| DLP Archive | ||
| All messages | Save all the messages that exceed the duplicate threshold in the DLP archive. | |
| First message only | Save the first message to exceed the duplicate threshold in the DLP archive. Subsequent messages that exceed the duplicate threshold will not be saved. | |
| Intercept | Messages that exceed the duplicate threshold are passed to the recipients, but if quarantine is enabled for intercepted messages, a copy of each message is also quarantined for later examination. If the quarantine of intercepted messages is disabled, the Intercept action has no effect. | |
| Block | Messages that exceed the duplicate threshold are blocked and will not be delivered to the message recipients. If quarantine is enabled for blocked messages, a copy of each blocked message is quarantined for later examination. | |
| Alert Notification | If the duplicate threshold is exceeded, the Carrier-enabled FortiGate unit will send an MMS duplicate message notification message. | |
Notifying duplicate message senders and receivers
The FortiOS Carrier unit does not send notifications to the sender or receiver of duplicate messages. If the sender or receiver is an attacker and is explicitly informed that they have exceeded a message threshold, the attacker may try to determine the exact threshold value by trial and error and then find a way around duplicate message protection. For this reason, no notification is set to the sender or receiver.
However, the FortiOS Carrier unit does have replacement messages for sending reply confirmations to MM1 senders and receivers and for MM4 senders for blocked messages identified as duplicate messages. For information about how FortiOS Carrier responds when message flood detection blocks a message, see and MMS duplicate messages and message floods.
Responses to MM1 senders and receivers
When the FortiOS Carrier unit identifies an MM1 message sent by a sender to an MMSC as a duplicate message and blocks it, the FortiOS Carrier unit returns a message submission confirmation (m-send.conf) to the sender (otherwise the sender’s handset would keep retrying the message). The m-send.conf message is sent only when the MM1 duplicate message action is set to Block. For other duplicate message actions the message is actually delivered to the MMSC and the MMSC sends the m-send.conf message.
Notifying duplicate message senders and receivers
You can customize the m-send.conf message by editing the MM1 send-conf duplicate message MM1 replacement message (from the CLI the mm1-send-conf-dupe replacement message). You can customize the response status and message text for this message. The default response status is “Content not accepted”. To hide the fact that the FortiOS Carrier unit is responding to a duplicate message, you can change the response status to “Success”. The default message text informs the sender that the message was blocked. You could change this to something more generic.
For example, the following command sets the submission confirmation response status to “Success” and changes the message text to “Message Sent OK”:
config system replacemsg mm1 mm1-send-conf-dupe set rsp-status ok set rsp-text “Message Sent OK”
end
When the FortiOS Carrier unit identifies an MM1 message received by a receiver from an MMSC as a duplicate message and blocks it, the FortiOS Carrier unit returns a message retrieval confirmation (m-retrieve.conf) to the sender (otherwise the sender’s handset would keep retrying). The m-retrieve.conf message is sent only when the MM1duplicate message action is set to Block. For other message flood actions the message is actually received by the receiver, so the MMSC sends the m-retrieve.conf message.
You can customize the m-retrive.conf message by editing the MM1 retrieve-conf duplicate message MM1 replacement message (from the CLI the mm1-retr-conf-dupe replacement message). You can customize the class, subject, and message text for this message.
For example, you could use the following command make the response more generic:
config system replacemsg mm1 mm1-retr-conf-dupe set subject “Message blocked”
set message “Message temporarily blocked by carrier”
end
Forward responses for duplicate MM4 messages
When the FortiOS Carrier unit identifies an MM4 message as a duplicate message and blocks it, the FortiOS Carrier unit returns a message forward response (MM4_forward.res) to the forwarding MMSC (otherwise the forwarding MMSC would keep retrying the message). The MM4_forward.res message is sent only when the MM4 duplicate message action is set to Block and the MM4-forward.req message requested a response. For more information, see and MMS duplicate messages and message floods.
You can customize the MM4_forward.res message by editing the MM4 duplicate message MM4 replacement message (from the CLI the mm4-dupe replacement message). You can customize the response status and message text for this message. The default response status is “Content not accepted” (err-content-notaccept). To hide the fact that the FortiOS Carrier unit is responding to a duplicate message, you can change the response status to “Success”. The default message text informs the sender that the message was blocked. You could change this to something more generic.
For example, the following command sets the submission confirmation response status to “Success” and changes the message text to “Message Forwarded OK”:
config system replacemsg mm4 mm4-dupe set rsp-status ok
set rsp-text “Message Forwarded OK” end
Viewing DLP archived messages