Technical Tip: How to permanently block SSL VPN failed logins using an Automation Stitch

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Description	This article describes how to make an Automation stitch that monitors and adds remote IP addresses associated with failed SSL VPN logins to a permanent block list.
Scope	FortiGate, SSL VPN.
Solution	The FortiGate does already have tools (enabled by default) that allow it to block a given source IP address if it fails to login to the SSL VPN successfully within a configurable time window. For more information on these tools/timers, see the following KB article: Technical Tip: SSL VPN timers explanation and SSL-VPN Login Attempt Limit (aka 'Lockout'). With that being said, the above timers will only block a given offending source IP for a temporary period, after which the offending IP address may attempt to log in again (and possibly re-trigger the lockout). To make a permanent block list (i.e. an offender is put on the list and must be manually removed), it is possible to use an Automation Stitch that monitors for SSL VPN log events and auto-updates an Address Group list with a list of blocked addresses. Warning: This method will result in permanent bans for a given Source IP address unless an admin manually intervenes. It is recommended to adjust the SSL VPN lockout settings so that normal users are not likely to be caught in this permanent ban (e.g. increase login-attempt-limit so that it takes more failed attempts before a ban is triggered). Creating an Address Group for Blocked Source IP Addresses. To do this in the GUI: Navigate to Policy & Objects -> Addresses, then select Create New -> Address Group. In later FortiOS versions (7.4 and later) select the Address Group button at the top of the page, then select Create New. Set a Name for the new Address Group object. In this article, the example Address Group will be named 'VPN_Failed_Login'. No additional configuration is required at this step. Select the OK button to complete the configuration. To do this in the CLI: config firewall addrgrp edit VPN_Failed_Login end Creating the Automation Stitch (Part 1: Stitch and Trigger). Navigate to Security Fabric -> Automation -> Stitch, then select Create New. Specify a name for the new Automation Stitch. This example will use 'SSL_VPN_Login_Block' for the name of the Automation Stitch itself. Next, select Add Trigger, then select the Create button in the top-right of the slide-out menu, followed by selecting FortiOS Event Log. Specify a name, then select the Event field and add the 'SSL VPN login fail' log entry (ID 39426) This example uses 'SSL_Login_Fail' as the name of the Automation Trigger. Select OK to complete the Trigger creation, then select the new Trigger and select Apply. Note: Instead of FortiOS Event logs, it is also possible to leverage the FortiAnalyzer Event Handler. Can be used to get more options compared to FortiOS Event logs in case of using FortiAnalyzer for logging. Refer to this article for setting up FortiAnalyzer Event Handler: Technical Tip: Enhance SSL VPN Security by blocking offenders' IP addresses using FortiAnalyzer Even... Creating the Automation Stitch (Part 2: Action and Finish Stitch). 5. In the same Automation Stitch, select Add Action, then select Create, followed by selecting CLI Script. 6. Specify the name ('BAN-SSLVPN-IP' is used in this example), then enter the following in the Script section: config firewall address edit SSLVPN-Block-%%log.remip%% set color 6 set subnet %%log.remip%%/32 end config firewall addrgrp     edit VPN_Failed_Login     append member SSLVPN-Block-%%log.remip%% end Note1: The above script, when paired with the FortiOS Event Log action, extracts the logged remote IP address and creates an Address Object for it, followed by adding the Address object to the Address Group. Note2:  The maximum number of members added to the address group is dependent on the OS version and model. In the below example, the maximum value is 600, and if the FortiGate receives a number of failed SSL VPN connections above 600, it creates the address object but cannot add to the address group. 7. Specify an Administrator profile of a super_admin (or another profile that has permission to create and modify Address objects/groups), then select OK, followed by Apply (to set the Action in the Stitch) and OK (to finalize the configuration for the Automation Stitch). Note: If the FortiGate has multi-VDOM enabled then the script needs to also specify the VDOM that the Address Group and SSL VPN are located in. In that case, add the following to the top of the script: config vdom     edit <vdom> [rest of the script follows] A complete Automation Stitch will look like this: Use the Address Group to block incoming SSL VPN connections (two methods available): Method 1: Set source-address and source-address-negate in SSL VPN settings. This method sets the Address Group in the SSL VPN settings for the source-address filter, then it pairs with set source-address-negate enable config option. This results in the SSL VPN matching all incoming Source IP addresses that are not in the Address Group: config vpn ssl settings     set source-address "VPN_Failed_Login"     set source-address-negate enable end Note : make sure to add a dummy address into "VPN_Failed_Login" address group as it will not work with empty address group ** Method 2: Create a Deny Local-In Policy with the Address Group in the Source Address field. This method results in the creation of a local-in policy (which filters incoming traffic destined for the FortiGate itself) that denies traffic sourced from the specified Address Group. This can be useful if more flexible rules are needed compared to Method 1 (i.e. blocking/allowing SSL VPN traffic using multiple different sets of addresses): config firewall local-in-policy edit 1 set intf <SSL VPN Listening interface> <----- The source-interface under SSL VPN settings. set srcaddr "VPN_Failed_Login" set srcaddr-negate disable set dstaddr "all" set dstaddr-negate disable set action deny set service "ALL" set service-negate disable set schedule "always" set status enable next end The Result: This stitch will add the remote-ip to the blocked address group on the first attempt itself so if that connection is legitimate then might have to remove it manually from the group so that the user can connect again. After that, the Address Object will be added to the Address Group created at the start, and that Address Group will be checked for blocking incoming connections (either with the SSL VPN setting in Method 1 and/or the local-in policy for Method 2). Note: The address group has a limit of 600 IPs, the group needs to be manually swapped with a new group once it is full. If the attack persistence is higher, further measures need to be taken. Maximum Values Table Related articles: SSL VPN security best practices  Restrict unauthorized access on the SSL VPN service Restricting SSL VPN connectivity from certain countries using firewall geography addresses  How to block SSL VPN Connection from a certain source IP Address