IPS custom pattern syntax

Keyword Value Usage
srcaddr/dstaddr <ipaddress>; The source/destination IP address
srcport/dstport <Number>; The source/destination port
content “<content string>;”

A string quoted within double quotes.

 Multiple contents can be specified in one rule. The value can contain mixed text and binary data. The binary data is generally enclosed within the pipe (|) character.

nocase

Can be used with content keyword only

 NULL Ignore case in the content value

rawbytes

Can be used with content keyword only		 NULL Ignore any decoding. Look at the raw packet data.

depth

Can be used with content keyword only

 <number>;

for example, depth:5;

 Look for the contents within the specified number of bytes of the payload. If the value of the depth keyword is smaller than the length of the value of the content keyword, this signature will never be matched.

offset

Can be used with content keyword only

 <number>;

for example, content:cgi-bin/phf;offset:4;depth:20;

 Start looking for the contents after the specified number of bytes of the payload. This tag is an absolute value in the payload. Follow the offset tag with the depth tag to stop looking for a match after the value specified by the depth tag. If there is no depth specified, continue looking for a match until the end of the payload.

distance

Can be used with content keyword only

 <number>;

for example, content:“ABC”; content:“DEF”; distance:1;

 Search for the contents the specified number of bytes relative to the end of the previously matched contents. The distance tag could be followed with the within tag. If there is no value specified for the within tag, continue looking for a match until the end of the payload.

within

Can be used with content keyword only		 <number>;

for example, content: “ABC”; content: “DEF”; within:10;

 Look for the contents within the specified number of bytes of the payload. Use with the distance tag.
uricontent uricontent:<content string>;

for example, uricontent:“%3F”;

 Search for the normalized request URI field. Binary data can be defined as the URI value.
isdataat <value> [,relative];

for example, content: “PASS”; isdataat: 50, relative;

 Verify that the payload has data at a specified location. Optionally look for data relative to the end of the previous content match.
pcre pcre:[!]“(/<regex>/|m/<regex>/)[ismxAEGRUB]”;

for example, pcre:“/BLAH/i”;

 The pcre keyword allows rules to be written using perl compatible regular expressions.

i - Case insensitive

s - Include newlines in the dot metacharacter

m - By default, the string is treated as one big line of characters^ and $ match at the start and end of the string. When m is set, ^ and $ match immediately following or immediately before any newline in the buffer, as well as the very start and very end of the buffer.

x - Whitespace data characters in the pattern are ignored except when escaped or inside a character class

A - The pattern must match only at the start of the buffer (same as ^)

E - Set $ to match only at the end of the subject string. Without E, $ also matches immediately before the final character if it is a newline (but not before any other newlines)

G - Inverts the “greediness” of the quantifiers so that they are not greedy by default, but become greedy if followed by “?”

R - Match relative to the end of the last pattern match (similar to distance:0;) U Match the decoded URI buffers (similar to the uri keyword)

B - Do not use the decoded buffers (similar to the raw keyword)
byte_test <bytes to convert>, [!]<operator>, <value>, <offset> [,relative] [,<endian>] [,<number type>, string]; oct,dec,hex used with string only

for example, msg: “AMD procedure 7 plog overflow”; content:“|00 04 93 F3|”; content:“|00 00 00 07|”; distance: 4.within:4; byte_test:4,>,1000,20,relative;

 Test a byte field against a specific value (with operator). Capable of testing binary values or converting representative byte strings to their binary equivalent and testing them. bytes_to_convert - The number of bytes to pick up from the packet operator - The operation to perform to test the value (<,>,=,!,&)

value - The value to test the converted value against

offset - The number of bytes into the payload to start processing

relative - Use an offset relative to last pattern match

big - Process the data as big

endian (default) little - Process the data as little endian

string - The data is stored in string format in the packet

hex - The converted string data is represented in hexadecimal

dec - The converted string data is represented in decimal

oct - The converted string data is represented in octal
byte_jump <bytes_to_convert>, <offset> [,relative] [,multiplier <multiplier value>] [,big] [,little][,string] [,hex] [,dec] [,oct] [,align] [,from_beginning]; oct,dec,hex used with string only

for example, content:“|00 00 00 01|”; distance: 4; within: 4; byte_jump: 4,12,relative,align

 bytes_to_convert - The number of bytes to pick up from the packet. multiplier value - multiply the number of calculated bytes by value and skip forward that number of byte

operator - The operation to perform to test the value (<,>,=,!,&)

value - The value to test the converted value against

offset - The number of bytes into the payload to start processing

relative - Use an offset relative to last pattern match

big - Process the data as big

endian (default) little - Process the data as little endian

string - The data is stored in string format inthe packet

hex - The converted string data is represented in hexadecimal

dec - The converted string data is represented in decimal

oct - The converted string data is represented in octal

align – round the number of converted bytes upto the next 32 bit boundary

from_beginning – Skip forward from the beginning of the packet payload instead of from the current position in the packet
ttl <number>;><number>;<<number>; Check the IP time-to-live value against the specified value
tos <number>; Check the IP TOS field for the specified value
id <number>; Check the IP ID field for the specified value
ipopts {rr | eol | nop | ts | sec | lsrr |ssrr | satid | any}

rr - Check if IP RR (record route) option is present

eol - Check if IP EOL (end of list) option is present

nop - Check if IP NOP (no op) option is present

ts - Check if IP TS (time stamp) option is present

sec - Check if IP SEC (IP security) option is present

lsrr - Check if IP LSRR (loose source routing) option is present

ssrr - Check if IP SSRR (strict source routing) option is present

satid - Check if IP SATID (stream identifier) option is present

any - Check if IP any option is present
fragoffset <number>; Allows to compare the IP fragment offset field against the decimal value
fragbits [+*!]<[MDR]>; Check if IP fragmentation and reserved bits are set in the IP header.

M - The More Fragments bit

D - The “Don’t Fragment” bit

R - The Reserved Bit

+ - Match on the specified bits, plus any others

* - Match if any of the specified bits are set

! - Match if the specified bits are not set
dsize [<|>] <number>[ <> number];

for example, dsize:300<>400;

 Test the packet payload size. With data_size specified, packet reassembly is turned off automatically so a signature with data_size and only_stream values set is wrong. dsize will fail on stream rebuilt packets, regardless of the size of the payload
flags [!|*|+]<FSRPAU120>[,<FSRPAU120>];

for example, flags:SF,12

 Specify the TCP flags to match in a packet.

S - Match the SYN flag

A - Match the ACK flag

F - Match the FIN flag

R - Match the RST flag

U - Match the URG flag

P - Match the PSH flag

1 - Match reserved bit

1 2 - Match reserved bit

2 0 - Match No TCP flags set

+ - Match on the specified bits, plus any others

* - Match if any of the specified bits are set

! - Match if the specified bits are not set
flow to_client|to_server|from_client| from_server ]; established; bi_direction; [no_stream|only_stream]; TCP only. The to_server value is equal to the from_client value. The to_client value is equal to the from_server value. The bi_direction tag makes the signature match traffic for both directions. For example, if you have a signature with “--dst_port 80”, and with bi_direction set, the signature checks traffic from and to port 80.
seq <number>; Check for the specified TCP sequence number
ack <number>; Check for the specified TCP acknowledge number
window <number>; Check for the specified TCP window size
itype [<|>]<number>[<>number]; Specify the ICMP type to match
icode [<|>]<number>[<>number]; Specify the ICMP code to match
icmp_id <number>; Check for the specified ICMP ID value
icmp_seq <number>; Check for the specified ICMP sequence value
rpc <application number>,[<version number>|*],[<procedure number>|*>; Check for RPC application, version,and procedure numbers in SUNRPCCALL requests. The * wildcard can be used for version and procedure numbers.
ip_proto <number>;[!]<number>;><number>;<<number>; Check the IP protocol header
samip NULL The source and the destination have the same IP addresses