Fortinet IPS manual Creating custom signatures

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Creating custom signatures

Custom signatures

Use the --protocol tcp keyword to limit the effect of the custom signature to only TCP traffic. This will save system resources by not unnecessarily scanning UDP and ICMP traffic.

F-SBID( --name "Block.SMTP.VRFY.CMD"; --pattern "vrfy"; --service SMTP; --protocol tcp; )

The FortiGate unit will limit its search for the pattern to TCP traffic and ignore the pattern in UDP and ICMP network traffic.

6Ignoring case sensitivity

By default, patterns are case sensitive. If a user directed his or her browser to Example.com, the custom signature would not recognize the URL as a match.

Use the --no_casekeyword to make the pattern matching case insensitive.

F-SBID( --name "Block.SMTP.VRFY.CMD"; --pattern "vrfy"; --service SMTP; --no_case; )

Unlike all of the other keywords in this example, the --no_casekeyword has no value. Only the keyword is required.

7Specifying the context

The SMTP vrfy command will appear in the SMTP header. The

--context host keyword/value pair allows you to limit the pattern search to only the header.

F-SBID( --name "Block.SMTP.VRFY.CMD"; --pattern "vrfy"; --service SMTP; --no_case; --context header; )

	FortiGate IPS User Guide Version 3.0 MR7
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Contents E R G U I D E Trademarks Contents Protocol decoders IPS sensorsDoS sensors SYN flood attacksIntroduction FortiGate IPSAbout this document Fortinet documentationDocument conventions Typographic conventionsFortiGate Pptp VPN User Guide Customer service and technical support Fortinet Knowledge CenterComments on Fortinet technical documentation IPS overview and general configuration IPS settings and controlsThis section contains the following topics When to use IPS Default signature and anomaly settingsDefault fail open setting Config ips global Set fail-open enable disable endSetting the buffer size Configuring logging and alert emailMonitoring the network and dealing with attacks Controlling sessionsAttack log messages Signature Anomaly FortiGuard CenterUsing IPS sensors in a protection profile Creating a protection profile that uses IPS sensorsAdding protection profiles to firewall policies Select Create NewAdding protection profiles to user groups Using IPS sensors in a protection profile Predefined signatures IPS predefined signaturesViewing the predefined signature list Settings EnableColumn Clear All FiltersCreate a sensor and add IPS filters to it Viewing the predefined signature list Custom signatures IPS custom signaturesViewing the custom signature list Custom signature configuration Adding custom signatures using the web-based managerAdding custom signatures using the CLI Command syntax patternCreating custom signatures Custom signature fieldsShows the valid characters for custom signature fields Custom signature syntax AttackidName BufferOverflow SrcportContent keywords Keyword and value Description Deprecated, see pattern and context keywords Pattern GET Context uriPattern yahoo.com Context hostPcre Regex/mdelimRegexdelimismxAEGRU Uri !uristrProtocol tcp IP header keywords Keyword and Value DescriptionTCP header keywords Keyword and Value Description Tcpflags AP Tcpflags S,12UDP header keywords Keyword and Value Description Icmp keywords Keyword and Value UsageOther keywords Keyword and Value Description Example 1 signature to block access to example.com Example custom signaturesSbid --name Block.example.com Sbid --name Block.example.com Example 2 signature to block the Smtp ‘vrfy’ command Sbid --name Block.SMTP.VRFY.CMDSbid --name Block.SMTP.VRFY.CMD --pattern vrfy Creating custom signatures Protocol decoders Protocol decodersUpgrading the IPS protocol decoder list Viewing the protocol decoder list Protocol decoder list Protocols Protocol decoder names PortAlldefault AlldefaultpassIPS sensors Viewing the IPS sensor listConfiguring IPS sensors Adding an IPS sensorProtectclient ProtectemailserverIPS sensor attributes IPS sensor filtersConfiguring filters ResetIPS sensor overrides Delete and Edit Delete or edit the filter IconsConfiguring pre-defined and custom overrides ApplicationExempt IP SourceDoS sensors Configuring DoS sensors Viewing the DoS sensor listSequence in which the sensors examine network traffic Appears, and select OKAnomaly configuration DoS sensor attributesName Enter or change the DoS sensor name Comments Will appear in the DoS sensor listUnderstanding the anomalies Anomaly Description Tcpdstsession UdpfloodUdpscan UdpsrcsessionUnderstanding the anomalies What is a SYN flood attack? SYN flood attacksHow SYN floods work What is SYN threshold? What is SYN proxy?FortiGate IPS Response to SYN flood attacks How IPS works to prevent SYN floodsIPS operation before synflood threshold is reached Configuring SYN flood protection Suggested settings for different network conditionsConfigure the options for tcpsynflood Select OK What is an Icmp sweep? Icmp sweep attacksHow Icmp sweep attacks work FortiGate IPS response to Icmp sweep attacksPredefined Icmp signatures Icmp sweep anomalies Configuring Icmp sweep protection Index FortiGate Version 3.0 MR7 IPS User GuideTechnical support