SIP message inspection and filtering

There are two types of VoIP profiles that can be configured:

config voip profile
    edit <name>
        set feature-set {ips | voipd}
    next
end

feature-set {ips | voipd}

Set the inspection feature set. ips: use the IPS Engine feature set for the ips-voip-filter firewall policy option. voipd: use the SIP ALG feature set for voip-profile firewall policy option.

SIP ALG provides users with security features to inspect and control SIP messages that are transported through the FortiGate, including:

• Verifying the SIP message syntax.
• Blocking particular types of SIP requests.
• Restricting the rate of particular SIP requests.

Proxy-based SIP ALG (feature-set voipd) is also able to handle features such as pin hole creation and NAT that flow-based SIP inspection cannot. Flow-based SIP (feature-set ips) can handle features such as MSRP decoding and scanning that proxy-based SIP ALG cannot.

The two VoIP profile types can be configured separately or at the same time on a firewall policy:

config firewall policy
    edit 1
        set voip-profile "voip_sip_alg"
        set ips-voip-filter "voip_sip_ips"
    next
end

Where:

• voip-profile can select a voip-profile with feature-set voipd.
• ips-voip-filter can select a voip-profile with feature-set ips.

The IPS-based VoIP profile (ips-voip-filter) allows flow-based SIP to complement SIP ALG while working together.

When both SIP ALG and SIP IPS are used and configured with same block rules, SIP IPS will take priority and do the blocking.

Unlike previous versions (7.0 and 7.2.0-7.2.4) where the firewall policy’s inspection mode determines whether the SIP traffic is scanned by SIP ALG or flow-based SIP, the inspection mode does not matter in this version. A voipd-based VoIP profile will activate SIP ALG inspection, while an ips-based VoIP profile will activate IPS-based SIP inspection. A voip-profile can be selected regardless of the inspection-mode used in the firewall policy.

For more information about the difference between SIP ALG and the SIP session helper, see SIP ALG and SIP session helper.

Example

In this example, SIP ALG is required for pinhole creation, handling NAT, and controlling SIP messages that requires flow-based SIP. The administrator needs to configure two SIP profiles, one with each feature set (voipd and ips), and apply these SIP profiles in the same firewall policy.

To configure SIP ALG with SIP IPS:

1. Configure the VoIP profiles:

   config voip profile
       edit "voip_sip_alg"
           set feature-set voipd
           set comment "sip_alg_simple"
           config sip
               set log-violations enable
               set log-call-summary enable
           end
       next
       edit "voip_sip_ips"
           set feature-set ips
           set comment "ips_voip_blocking"
           config sip
               set block-invite enable
               set log-violations enable
           end
       next
   end

2. Configure the firewall policy:

   config firewall policy
       edit 1
           set srcintf "port1"
           set dstintf "port9"
           set action accept
           set srcaddr "all"
           set dstaddr "all"
           set srcaddr6 "all"
           set dstaddr6 "all"
           set schedule "always"
           set service "ALL"
           set utm-status enable
           set inspection-mode proxy
           set ips-sensor "g-default"
           set voip-profile "voip_sip_alg"
           set ips-voip-filter "voip_sip_ips"
           set logtraffic all
           set nat enable
       next
   end

To verify the SIP proxy SIP calls:

1. Verify the register request:

   # diagnose sys sip-proxy calls
   sip calls
     vdom 1 (vdom1) vrf 0 call 7f2b99828300
       call-id: 619216389
       txn 7f2b998ad600 (REGISTER)
         cseq 2 dir 0 state 5 status 200 expiry 527 HA 0
         i_session: 7f2b998aac00  r_session: 7f2b998aac00
         register: present
         from: sip:2001@172.16.200.44
         to: sip:2001@172.16.200.44
         src: 10.1.100.11:5060
         dst: 172.16.200.44:5060

2. Verify the invite request:

   # diagnose sys sip-proxy calls
   sip calls
     vdom 1 (vdom1) vrf 0 call 7f2b99828300
       call-id: 619216389
       txn 7f2b998ad600 (REGISTER)
         cseq 2 dir 0 state 5 status 200 expiry 316 HA 0
         i_session: 7f2b998aac00  r_session: 7f2b998aac00
         register: present
         from: sip:2001@172.16.200.44
         to: sip:2001@172.16.200.44
         src: 10.1.100.11:5060
         dst: 172.16.200.44:5060

Sample logs

Register request:

date=2023-01-13 time=09:46:03 eventtime=1673631963477298677 tz="-0800" logid="0814044032" type="utm" subtype="voip" eventtype="voip" level="information" vd="vdom1" session_id=17092 epoch=0 event_id=1 srcip=10.1.100.11 src_port=5060 dstip=172.16.200.44 dst_port=5060 proto=17 src_int="port1" dst_int="port9" policy_id=1 profile="voip_sip_alg" voip_proto="sip" kind="register" action="permit" status="succeeded" duration=0 dir="session_origin" call_id="619216389" from="sip:2001@172.16.200.44" to="sip:2001@172.16.200.44"

Invite request:

date=2023-01-13 time=09:54:43 eventtime=1673632484065549240 tz="-0800" logid="0814044033" type="utm" subtype="voip" eventtype="voip" level="notice" vd="vdom1" session_id=17092 epoch=0 event_id=0 srcip=10.1.100.11 src_port=5060 dstip=172.16.200.44 dst_port=5060 proto=17 src_int="port1" dst_int="port9" policy_id=1 profile="voip_sip_ips" voip_proto="sip" kind="call" action="block" status="N/A" reason="block-request" duration=0 dir="session_reverse" message_type="request" request_name="INVITE" call_id="1967779864" count=0 from="<sip:2001@172.16.200.44>" to="<sip:2002@172.16.200.44>" attackid=50083 attack="SIP.Invite.Method"

SIP message syntax inspection

For syntax verification, the following attributes are available for configuration in the VoIP profile to determine what action is taken when a specific syntax error or attack based on invalid syntax is detected. For example, the action can be set to pass or discard it.

malformed-request-line
malformed-header-via
malformed-header-from
malformed-header-to
malformed-header-call-id
malformed-header-cseq
malformed-header-rack
malformed-header-rseq
malformed-header-contact
malformed-header-record-route
malformed-header-route
malformed-header-expires
malformed-header-content-type
malformed-header-content-length
malformed-header-max-forwards
malformed-header-allow
malformed-header-p-asserted-identity
malformed-header-sdp-v
malformed-header-sdp-o
malformed-header-sdp-s
malformed-header-sdp-i
malformed-header-sdp-c
malformed-header-sdp-b
malformed-header-sdp-z
malformed-header-sdp-k
malformed-header-sdp-a
malformed-header-sdp-t
malformed-header-sdp-r
malformed-header-sdp-m
malformed-header-no-require*
malformed-header-no-proxy-require*

* = only available in flow mode

SIP message blocking

The following options are available in the VoIP profile to block SIP messages:

block-long-lines
block-unknown
block-ack  
block-bye  
block-cancel   
block-info     
block-invite   
block-message  
block-notify   
block-options  
block-prack    
block-publish  
block-refer    
block-register 
block-subscribe
block-update   
block-geo-red-options**

** = only available in proxy mode

SIP message rate limiting

The rate of certain types of SIP requests that are passing through the SIP ALG can be restricted:

register-rate       
invite-rate         
subscribe-rate      
message-rate        
notify-rate         
refer-rate          
update-rate         
options-rate        
ack-rate            
prack-rate          
info-rate           
publish-rate        
bye-rate            
cancel-rate 

Additionally, flow-based SIP supports the following rate tracking features:

register-rate-track none
invite-rate-track none
subscribe-rate-track none
message-rate-track none
notify-rate-track none
refer-rate-track none
update-rate-track none
options-rate-track none
ack-rate-track none
prack-rate-track none
info-rate-track none
publish-rate-track none
bye-rate-track none
cancel-rate-track none

Call-Id and Content-Type regex

When the ips VoIP profile feature set is selected, options for Call-Id and Content-Type header values can be configured.

config voip profile
    edit <name>
        config sip
            set call-id-regex <string>
            set call-id-regex <string>
        end
    next
end

call-id-regex <string>	Enter a validation PCRE regular expression for the Call-Id header value.
call-id-regex <string>	Enter a validation PCRE regular expression for the Content-Type header value.