6.13. HTTP Keywords¶

Using the HTTP specific sticky buffers provides a way to efficiently inspect specific fields of the HTTP protocol. After specifying a sticky buffer in a rule it should be followed by one or more doc:payload-keywords.

Many of the sticky buffers have legacy variants in the older “content modifier” notation. See Modifier Keywords for more information. As a refresher:

‘sticky buffers’ are placed first and all keywords following it apply to that buffer, for instance:
```
alert http any any -> any any (http.response_line; content:"403 Forbidden"; sid:1;)
```
Sticky buffers apply to all “payload” keywords following it. E.g. content, isdataat, byte_test, pcre.
‘content modifiers’ look back in the rule, e.g.:
```
alert http any any -> any any (content:"index.php"; http_uri; sid:1;)
```
Content modifiers only apply to the preceding content keyword.

The following request keywords are available:

Keyword	Legacy Content Modifier	Direction
http.uri	http_uri	Request
http.uri.raw	http_raw_uri	Request
http.method	http_method	Request
http.request_line	http_request_line (*)	Request
http.request_body	http_client_body	Request
http.header	http_header	Both
http.header.raw	http_raw_header	Both
http.cookie	http_cookie	Both
http.user_agent	http_user_agent	Request
http.host	http_host	Request
http.host.raw	http_raw_host	Request
http.accept	http_accept (*)	Request
http.accept_lang	http_accept_lang (*)	Request
http.accept_enc	http_accept_enc (*)	Request
http.referer	http_referer (*)	Request
http.connection	http_connection (*)	Request
http.content_type	http_content_type (*)	Both
http.content_len	http_content_len (*)	Both
http.start	http_start (*)	Both
http.protocol	http_protocol (*)	Both
http.header_names	http_header_names (*)	Both

*) sticky buffer

The following response keywords are available:

Keyword	Legacy Content Modifier	Direction
http.stat_msg	http_stat_msg	Response
http.stat_code	http_stat_code	Response
http.response_line	http_response_line (*)	Response
http.header	http_header	Both
http.header.raw	http_raw_header	Both
http.cookie	http_cookie	Both
http.response_body	http_server_body	Response
http.server	N/A	Response
http.location	N/A	Response
file.data	file_data (*)	Response
http.content_type	http_content_type (*)	Both
http.content_len	http_content_len (*)	Both
http.start	http_start (*)	Both
http.protocol	http_protocol (*)	Both
http.header_names	http_header_names (*)	Both

*) sticky buffer

6.13.1. HTTP Primer¶

It is important to understand the structure of HTTP requests and responses. A simple example of a HTTP request and response follows:

HTTP request

GET /index.html HTTP/1.0\r\n

GET is the request method. Examples of methods are: GET, POST, PUT, HEAD, etc. The URI path is /index.html and the HTTP version is HTTP/1.0. Several HTTP versions have been used over the years; of the versions 0.9, 1.0 and 1.1, 1.0 and 1.1 are the most commonly used today.

Example request with keywords:

HTTP	Keyword
GET /index.html HTTP/1.1\r\n	http.request_line
Host: www.oisf.net\r\n	http.header
Cookie: <cookie data>	http.cookie

Example request with finer grained keywords:

HTTP	Keyword
GET /index.html HTTP/1.1\r\n	http.method http.uri http.protocol
Host: www.oisf.net\r\n User-Agent: Mozilla/5.0\r\n	http.host
Host: www.oisf.net\r\n User-Agent: Mozilla/5.0\r\n	http.user_agent
Cookie: <cookie data>	http.cookie

HTTP response

HTTP/1.0 200 OK\r\n
<html>
<title> some page </title>
</HTML>

In this example, HTTP/1.0 is the HTTP version, 200 the response status code and OK the response status message.

Although cookies are sent in an HTTP header, you can not match on them with the http.header keyword. Cookies are matched with their own keyword, namely http.cookie.

Each part of the table belongs to a so-called buffer. The HTTP method belongs to the method buffer, HTTP headers to the header buffer etc. A buffer is a specific portion of the request or response that Suricata extracts in memory for inspection.

All previous described keywords can be used in combination with a buffer in a signature. The keywords distance and within are relative modifiers, so they may only be used within the same buffer. You can not relate content matches against different buffers with relative modifiers.

6.13.2. http.method¶

With the http.method content modifier, it is possible to match specifically and only on the HTTP method buffer. The keyword can be used in combination with all previously mentioned content modifiers such as: depth, distance, offset, nocase and within.

Examples of methods are: GET, POST, PUT, HEAD, DELETE, TRACE, OPTIONS, CONNECT and PATCH.

Example of a method in a HTTP request:

Example of the purpose of method:

6.13.3. http.uri and http.uri.raw¶

With the http.uri and the http.uri.raw content modifiers, it is possible to match specifically and only on the request URI buffer. The keyword can be used in combination with all previously mentioned content modifiers like depth, distance, offset, nocase and within.

The uri has two appearances in Suricata: the uri.raw and the normalized uri. The space for example can be indicated with the heximal notation %20. To convert this notation in a space, means normalizing it. It is possible though to match specific on the characters %20 in a uri. This means matching on the uri.raw. The uri.raw and the normalized uri are separate buffers. So, the uri.raw inspects the uri.raw buffer and can not inspect the normalized buffer.

Note

uri.raw never has any spaces in it. With this request line GET /uid=0(root) gid=0(root) HTTP/1.1, the http.uri.raw will match /uid=0(root) and http.protocol will match gid=0(root) HTTP/1.1 Reference: https://redmine.openinfosecfoundation.org/issues/2881

Example of the URI in a HTTP request:

Example of the purpose of http.uri:

6.13.4. uricontent¶

The uricontent keyword has the exact same effect as the http.uri content modifier. uricontent is a deprecated (although still supported) way to match specifically and only on the request URI buffer.

Example of uricontent:

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:”ET TROJAN Possible Vundo Trojan Variant reporting to Controller”; flow:established,to_server; content:”POST “; depth:5; uricontent:”/frame.html?”; urilen: > 80; classtype:trojan-activity; reference:url,doc.emergingthreats.net/2009173; reference:url,www.emergingthreats.net/cgi-bin/cvsweb.cgi/sigs/VIRUS/TROJAN_Vundo; sid:2009173; rev:2;)

The difference between http.uri and uricontent is the syntax:

When authoring new rules, it is recommended that the http.uri content sticky buffer be used rather than the deprecated uricontent keyword.

6.13.5. urilen¶

The urilen keyword is used to match on the length of the request URI. It is possible to use the < and > operators, which indicate respectively smaller than and larger than.

The format of urilen is:

urilen:3;

Other possibilities are:

urilen:1;
urilen:>1;
urilen:<10;
urilen:10<>20;        (bigger than 10, smaller than 20)

Example:

Example of urilen in a signature:

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:”ET TROJAN Possible Vundo Trojan Variant reporting to Controller”; flow:established,to_server; content:”POST “; depth:5; uricontent:”/frame.html?”; urilen: > 80; classtype:trojan-activity; reference:url,doc.emergingthreats.net/2009173; reference:url,www.emergingthreats.net/cgi-bin/cvsweb.cgi/sigs/VIRUS/TROJAN_Vundo; sid:2009173; rev:2;)

You can also append norm or raw to define what sort of buffer you want to use (normalized or raw buffer).

6.13.6. http.protocol¶

The http.protocol inspects the protocol field from the HTTP request or response line. If the request line is ‘GET / HTTP/1.0rn’, then this buffer will contain ‘HTTP/1.0’.

Example:

alert http any any -> any any (flow:to_server; http.protocol; content:"HTTP/1.0"; sid:1;)

http.protocol replaces the previous keyword name: `http_protocol. You may continue +to use the previous name, but it’s recommended that rules be converted to use +the new name.

Example:

alert http any any -> any any (flow:to_server; http.protocol; content:"HTTP/1.0"; sid:1;)

6.13.7. http.request_line¶

The http.request_line forces the whole HTTP request line to be inspected.

Example:

alert http any any -> any any (http.request_line; content:"GET / HTTP/1.0"; sid:1;)

6.13.8. http.header and http.header.raw¶

With the http.header content modifier, it is possible to match specifically and only on the HTTP header buffer. This contains all of the extracted headers in a single buffer, except for those indicated in the documentation that are not able to match by this buffer and have their own content modifier (e.g. http.cookie). The modifier can be used in combination with all previously mentioned content modifiers, like depth, distance, offset, nocase and within.

Note: the header buffer is normalized. Any trailing whitespace and tab characters are removed. See: https://lists.openinfosecfoundation.org/pipermail/oisf-users/2011-October/000935.html. If there are multiple values for the same header name, they are concatenated with a comma and space (”, “) between each of them. See RFC 2616 4.2 Message Headers. To avoid that, use the http.header.raw keyword.

Example of a header in a HTTP request:

Example of the purpose of http.header:

6.13.10. http.user_agent¶

The http.user_agent content modifier is part of the HTTP request header. It makes it possible to match specifically on the value of the User-Agent header. It is normalized in the sense that it does not include the _”User-Agent: “_ header name and separator, nor does it contain the trailing carriage return and line feed (CRLF). The keyword can be used in combination with all previously mentioned content modifiers like depth, distance, offset, nocase and within. Note that the pcre keyword can also inspect this buffer when using the /V modifier.

Normalization: leading spaces are not part of this buffer. So “User-Agent: rn” will result in an empty http.user_agent buffer.

Example of the User-Agent header in a HTTP request:

Example of the purpose of http.user_agent:

6.13.10.1. Notes¶

The http.user_agent buffer will NOT include the header name, colon, or leading whitespace. i.e. it will not include “User-Agent: “.
The http.user_agent buffer does not include a CRLF (0x0D 0x0A) at the end. If you want to match the end of the buffer, use a relative isdataat or a PCRE (although PCRE will be worse on performance).
If a request contains multiple “User-Agent” headers, the values will be concatenated in the http.user_agent buffer, in the order seen from top to bottom, with a comma and space (”, “) between each of them.

Example request:
```
GET /test.html HTTP/1.1
User-Agent: SuriTester/0.8
User-Agent: GGGG
```
http.user_agent buffer contents:
```
SuriTester/0.8, GGGG
```
Corresponding PCRE modifier: V
Using the http.user_agent buffer is more efficient when it comes to performance than using the http.header buffer (~10% better).
https://blog.inliniac.net/2012/07/09/suricata-http_user_agent-vs-http_header/

6.13.11. http.accept¶

Sticky buffer to match on the HTTP Accept header. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (http.accept; content:"image/gif"; sid:1;)

6.13.12. http.accept_enc¶

Sticky buffer to match on the HTTP Accept-Encoding header. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (http.accept_enc; content:"gzip"; sid:1;)

6.13.13. http.accept_lang¶

Sticky buffer to match on the HTTP Accept-Language header. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (http.accept_lang; content:"en-us"; sid:1;)

6.13.14. http.connection¶

Sticky buffer to match on the HTTP Connection header. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (http.connection; content:"keep-alive"; sid:1;)

6.13.15. http.content_type¶

Sticky buffer to match on the HTTP Content-Type headers. Only contains the header value. The \r\n after the header are not part of the buffer.

Use flow:to_server or flow:to_client to force inspection of request or response.

Examples:

alert http any any -> any any (flow:to_server; \
        http.content_type; content:"x-www-form-urlencoded"; sid:1;)

alert http any any -> any any (flow:to_client; \
        http.content_type; content:"text/javascript"; sid:2;)

6.13.16. http.content_len¶

Sticky buffer to match on the HTTP Content-Length headers. Only contains the header value. The \r\n after the header are not part of the buffer.

Use flow:to_server or flow:to_client to force inspection of request or response.

Examples:

alert http any any -> any any (flow:to_server; \
        http.content_len; content:"666"; sid:1;)

alert http any any -> any any (flow:to_client; \
        http.content_len; content:"555"; sid:2;)

To do a numeric inspection of the content length, byte_test can be used.

Example, match if C-L is equal to or bigger than 8079:

alert http any any -> any any (flow:to_client; \
        http.content_len; byte_test:0,>=,8079,0,string,dec; sid:3;)

6.13.17. http.referer¶

Sticky buffer to match on the HTTP Referer header. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (http.referer; content:".php"; sid:1;)

6.13.18. http.start¶

Inspect the start of a HTTP request or response. This will contain the request/response line plus the request/response headers. Use flow:to_server or flow:to_client to force inspection of request or response.

Example:

alert http any any -> any any (http.start; content:"HTTP/1.1|0d 0a|User-Agent"; sid:1;)

The buffer contains the normalized headers and is terminated by an extra \r\n to indicate the end of the headers.

6.13.19. http.header_names¶

Inspect a buffer only containing the names of the HTTP headers. Useful for making sure a header is not present or testing for a certain order of headers.

Buffer starts with a \r\n and ends with an extra \r\n.

Example buffer:

\\r\\nHost\\r\\n\\r\\n

Example rule:

alert http any any -> any any (http.header_names; content:"|0d 0a|Host|0d 0a|"; sid:1;)

Example to make sure only Host is present:

alert http any any -> any any (http.header_names; \
        content:"|0d 0a|Host|0d 0a 0d 0a|"; sid:1;)

Example to make sure User-Agent is directly after Host:

alert http any any -> any any (http.header_names; \
        content:"|0d 0a|Host|0d 0a|User-Agent|0d 0a|"; sid:1;)

Example to make sure User-Agent is after Host, but not necessarily directly after:

alert http any any -> any any (http.header_names; \
        content:"|0d 0a|Host|0d 0a|"; content:"|0a 0d|User-Agent|0d 0a|"; \
        distance:-2; sid:1;)

6.13.20. http.request_body¶

With the http.request_body content modifier, it is possible to match specifically and only on the HTTP request body. The keyword can be used in combination with all previously mentioned content modifiers like distance, offset, nocase, within, etc.

Example of http.request_body in a HTTP request:

Example of the purpose of http.client_body:

Note: how much of the request/client body is inspected is controlled in the libhtp configuration section via the request-body-limit setting.

http.request_body replaces the previous keyword name: `http_client_body. You may continue +to use the previous name, but it’s recommended that rules be converted to use +the new name.

6.13.21. http.stat_code¶

With the http.stat_code content modifier, it is possible to match specifically and only on the HTTP status code buffer. The keyword can be used in combination with all previously mentioned content modifiers like distance, offset, nocase, within, etc.

Example of http.stat_code in a HTTP response:

Example of the purpose of http.stat_code:

6.13.22. http.stat_msg¶

With the http.stat_msg content modifier, it is possible to match specifically and only on the HTTP status message buffer. The keyword can be used in combination with all previously mentioned content modifiers like depth, distance, offset, nocase and within.

Example of http.stat_msg in a HTTP response:

Example of the purpose of http.stat_msg:

6.13.23. http.response_line¶

The http.response_line forces the whole HTTP response line to be inspected.

Example:

alert http any any -> any any (http.response_line; content:"HTTP/1.0 200 OK"; sid:1;)

6.13.24. http.response_body¶

With the http.response_body content modifier, it is possible to match specifically and only on the HTTP response body. The keyword can be used in combination with all previously mentioned content modifiers like distance, offset, nocase, within, etc.

Note: how much of the response/server body is inspected is controlled in your libhtp configuration section via the response-body-limit setting.

6.13.24.1. Notes¶

Using http.response_body is similar to having content matches that come after file_data except that it doesn’t permanently (unless reset) set the detection pointer to the beginning of the server response body. i.e. it is not a sticky buffer.
http.response_body will match on gzip decoded data just like file_data does.
Since http.response_body matches on a server response, it can’t be used with the to_server or from_client flow directives.
Corresponding PCRE modifier: Q
further notes at the file_data section below.

http.response_body replaces the previous keyword name: `http_server_body. You may continue +to use the previous name, but it’s recommended that rules be converted to use +the new name.

6.13.25. http.server¶

Sticky buffer to match on the HTTP Server headers. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (flow:to_client; \
        http.server; content:"Microsoft-IIS/6.0"; sid:1;)

6.13.26. http.location¶

Sticky buffer to match on the HTTP Location headers. Only contains the header value. The \r\n after the header are not part of the buffer.

Example:

alert http any any -> any any (flow:to_client; \
        http.location; content:"http://www.google.com"; sid:1;)

6.13.27. http.host and http.host.raw¶

With the http.host content modifier, it is possible to match specifically and only the normalized hostname. The http.host.raw inspects the raw hostname.

The keyword can be used in combination with most of the content modifiers like distance, offset, within, etc.

The nocase keyword is not allowed anymore. Keep in mind that you need to specify a lowercase pattern.

6.13.27.1. Notes¶

http.host does not contain the port associated with the host (i.e. abc.com:1234). To match on the host and port or negate a host and port use http.host.raw.
The http.host and http.host.raw buffers are populated from either the URI (if the full URI is present in the request like in a proxy request) or the HTTP Host header. If both are present, the URI is used.
The http.host and http.host.raw buffers will NOT include the header name, colon, or leading whitespace if populated from the Host header. i.e. they will not include “Host: “.
The http.host and http.host.raw buffers do not include a CRLF (0x0D 0x0A) at the end. If you want to match the end of the buffer, use a relative ‘isdataat’ or a PCRE (although PCRE will be worse on performance).
The http.host buffer is normalized to be all lower case.
The content match that http.host applies to must be all lower case or have the nocase flag set.
http.host.raw matches the unnormalized buffer so matching will be case-sensitive (unless nocase is set).
If a request contains multiple “Host” headers, the values will be concatenated in the http.host and http.host.raw buffers, in the order seen from top to bottom, with a comma and space (”, “) between each of them.

Example request:
```
GET /test.html HTTP/1.1
Host: ABC.com
Accept: */*
Host: efg.net
```
http.host buffer contents:
```
abc.com, efg.net
```
http.host.raw buffer contents:
```
ABC.com, efg.net
```
Corresponding PCRE modifier (http_host): W
Corresponding PCRE modifier (http_raw_host): Z

6.13.28. file_data¶

With file_data, the HTTP response body is inspected, just like with http.response_body. The file_data keyword is a sticky buffer.

Example:

alert http any any -> any any (file_data; content:"abc"; content:"xyz";)

The file_data keyword affects all following content matches, until the pkt_data keyword is encountered or it reaches the end of the rule. This makes it a useful shortcut for applying many content matches to the HTTP response body, eliminating the need to modify each content match individually.

As the body of a HTTP response can be very large, it is inspected in smaller chunks.

How much of the response/server body is inspected is controlled in your libhtp configuration section via the response-body-limit setting.

If the HTTP body is a flash file compressed with ‘deflate’ or ‘lzma’, it can be decompressed and file_data can match on the decompress data. Flash decompression must be enabled under libhtp configuration:

# Decompress SWF files.
# 2 types: 'deflate', 'lzma', 'both' will decompress deflate and lzma
# compress-depth:
# Specifies the maximum amount of data to decompress,
# set 0 for unlimited.
# decompress-depth:
# Specifies the maximum amount of decompressed data to obtain,
# set 0 for unlimited.
swf-decompression:
  enabled: yes
  type: both
  compress-depth: 0
  decompress-depth: 0

6.13.28.1. Notes¶

If a HTTP body is using gzip or deflate, file_data will match on the decompressed data.
Negated matching is affected by the chunked inspection. E.g. ‘content:!”<html”;’ could not match on the first chunk, but would then possibly match on the 2nd. To avoid this, use a depth setting. The depth setting takes the body size into account. Assuming that the response-body-minimal-inspect-size is bigger than 1k, ‘content:!”<html”; depth:1024;’ can only match if the pattern ‘<html’ is absent from the first inspected chunk.
file_data can also be used with SMTP

6.13. HTTP Keywords¶

6.13.1. HTTP Primer¶

6.13.2. http.method¶

6.13.3. http.uri and http.uri.raw¶

6.13.4. uricontent¶

6.13.5. urilen¶

6.13.6. http.protocol¶

6.13.7. http.request_line¶

6.13.8. http.header and http.header.raw¶

6.13.9. http.cookie¶

6.13.10. http.user_agent¶

6.13.10.1. Notes¶

6.13.11. http.accept¶

6.13.12. http.accept_enc¶

6.13.13. http.accept_lang¶

6.13.14. http.connection¶

6.13.15. http.content_type¶

6.13.16. http.content_len¶

6.13.17. http.referer¶

6.13.18. http.start¶

6.13.19. http.header_names¶

6.13.20. http.request_body¶

6.13.21. http.stat_code¶

6.13.22. http.stat_msg¶

6.13.23. http.response_line¶

6.13.24. http.response_body¶

6.13.24.1. Notes¶

6.13.25. http.server¶

6.13.26. http.location¶

6.13.27. http.host and http.host.raw¶

6.13.27.1. Notes¶

6.13.28. file_data¶

6.13.28.1. Notes¶