Snort 2 FortiGate

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    Usage: convert Snort rule into fortinet IPS signature format
    -i <input Snort rule txt>
    -o <output IPS rule txt>, default fortirules.txt
    -h or --help - This Usage
    -q quiet
    -j output rule txt in a json format
    -g output suitable for GUI entry
    -e only convert enabled signatures
    --no-all skip result for invalid lines in file
    --sig-max-len maximum length of converted IPS sig
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The Snort2Fortigate script provides a best-effort translation of Snort rules into FortiGate IPS Custom Signatures.

Usage

Input

• -i [file] or --input [file] (Required) A text file of Snort rules. Snort2 and Snort3 syntax are both accepted. See Supported Options for the full list of options we can convert at this time. Snort rules that are commented out (# alert tcp...) are also converted by default. This behaviour can be changed with option --enabled-only or -e.

Output

• -o [file] or --output [file] Defaults to fortirules.txt. A text file of IPS custom signatures, quotes-escaped to be usable in the CLI. Alternatively, use the provided options to generate without escaped quotes (-gfor use in GUI) and in JSON format with -j. JSON output format, for each parsed rule:

"converted": "The converted IPS signature",
"messages": [
    {
        "level": "WARNING or ERROR",
        "message": "Reason for failure."
    }
],
"name": "Name of the converted signature (also present in the signature itself)",
"original": "The original Snort rule",
"success": true if a signature was converted at all, or false if there is an ERROR and the rule is skipped

Additionally, the JSON output aggregates count of converted signatures:

"statistics": {
    "failure": 1,
    "success": 3
}

Additional Options

• -q or --quiet Suppress warnings and errors.
• -e or --enabled-only By default, all Snort rules found in the file are converted. Set this option to not convert Snort rules that are commented out with a single #, eg. rules beginning with # alert ....
• --no-all Set this option to ignore lines that do not begin with a rule action. Current supported rule actions: alert, log, pass, drop, reject, sdrop.

Logging

Unsupported or unrecognized options are logged as a warning and the rest of the signature is still generated. Use these signatures with discretion. Unacceptable errors in parsing the Snort syntax are logged as ERROR and the rule is skipped. The total number of converted IPS rules is printed: Total 6 from 7 Snort rules are converted. See Known Issues for common conversion issues.

Supported Options

Snort Option	FGT Conversion	Notes
content	--pattern	Snort3 content modifiers as suboptions accepted
pcre	--pcre
nocase	--no_case
distance	--distance
within	--within
depth	--within num,context
offset	--distance num,context
file_data	--context file
http_client_body	--context body
http_cookie	--context header
http_header	--context header
http_method	--context uri	When matching for "GET" or "POST" this is converted to --parsed_type HTTP_GET (or _POST)
http_raw_cookie	--context header
http_raw_header	--context header
http_raw_request	--context uri
http_raw_status	--context banner
http_raw_uri	--context uri
http_stat_code	--context banner
http_stat_msg	--context banner
http_uri	--context uri
http_user_agent	--context header
uricontent	--context uri
pkt_data	--context packet
raw_data	--context packet_origin
rawbytes	--context packet_origin
sip_body	--context body	--service sip is added to the rule
sip_header	--context header	--service sip is added to the rule
sip_method	--context banner	--service sip is added to the rule
sip_stat_code	--context banner	--service sip is added to the rule
dsize	--data_size	Does not support norm modifier
bufferlen	--data_size num,uri	Only when used inside http_uri sticky buffer (Snort 3)
urilen	--data_size num,uri
isdataat	--data_at
ssl_version	--parsed_type
service	--service	Only in Snort3. Can only handle one service In Snort2, service is in metadata
sameip	--same_ip
id	ip_id
ip proto	--protocol or --ip[offset]	If no operators present, --protocol is used If operators are present --ip[offset] is used.
ipopts	--ip_option	IP option esec is not supported
tos	--ip_tos	! operator is not supported
ttl	--ip.ttl
icmp_seq	--icmp_seq
icmp_id	--icmp_id
icode	--icmp.code
itype	--icmp.type
flow	--flow	Only support to_client, to_server, from_client, from_server.
seq	--seq
ack	--ack
flags	--tcp_flags
window	--window_size
flowbits	--tag cmd,tag_name	Support commands set, isset, isnotset, noalert, and toggle only. group_name is not supported
byte_extract	--extract	Does not support dce, bitmasks, and multiplier modifiers. Extracts to a register instead of variables (see Issues).
byte_jump	--byte_jump	Does not support dce, bitmasks, from_end, and post_offset modifiers.
byte_test	--byte_test	Does not support dce and bitmask modifiers. Does not support !& and !^ operators. Can only test against 1,2,4 bytes.
detection_filter	--rate count,sec --track filter

Known Issues

• Option fast_pattern does not have an IPS signature equivalent. IPS signatures are optimized by the engine for fast matching. This option is skipped silently.
• Snort variables (extracted by byte_extract in the same rule) are converted to registers to use within IPS signatures. IPS engine supports up to 8 registers at this time ($0-$7).
• For rules applying to more than one 'service' (metadata service (Snort2) or the 'service' keyword in Snort3), the resulting IPS signature will not include the service option as IPS signatures do not support having more than one service keyword per signature.
• IPS signatures do not support matching by hashes md5, sha256, or sha512.
• Content modifiers distance and within in Snort are to be used only after a preceding match in the same buffer. Otherwise, depth and offset should be used from the beginning of the buffer if there is no previous match.
• Keywords dsize, icode, itype, ip_proto, urilen, and byte_test cannot directly convert <=, >= operators. To mitigate this issue, the value is added/subtracted by 1 to complete the translation. This may result in failed conversions when overflow occurs during the operation.
• In the Snort rule headers, policy variables (eg. $OFFICE_NET) cannot be translated to its IP address as each environment is different.
• Custom signatures currently do not support multiple ports, eg. tcp any [80,8080].... The converted signature will omit the list of ports (with warning).

Running Tests

Some test cases of sample Snort signatures and the equivalent valid IPS output are included. To run unit tests, use: ./test/test_snort2fortigate.py

Support

Fortinet-provided scripts in this and other GitHub projects do not fall under the regular Fortinet technical support scope and are not supported by FortiCare Support Services. For direct issues, please refer to the Issues tab of this GitHub project. For other questions related to this project, contact github@fortinet.com.

License

License © Fortinet Technologies. All rights reserved.