Variables
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## Variables

The following variables are supported in ModSecurity 2.x:

### `ARGS`

`ARGS` is a collection and can be used on its own (means all arguments including the POST Payload), with a static parameter (matches arguments with that name), or with a regular expression (matches all arguments with name that matches the regular expression). To look at only the query string or body arguments, see the `ARGS_GET` and `ARGS_POST` collections.

Some variables are actually collections, which are expanded into more variables at runtime. The following example will examine all request arguments:

    SecRule ARGS dirty

Sometimes, however, you will want to look only at parts of a collection. This can be achieved with the help of the selection operator(colon). The following example will only look at the arguments named`p` (do note that, in general, requests can contain multiple arguments with the same name):

    SecRule ARGS:p dirty

It is also possible to specify exclusions. The following will examine all request arguments for the word dirty, except the ones named `z` (again, there can be zero or more arguments named`z`):

    SecRule ARGS|!ARGS:z dirty

There is a special operator that allows you to count how many variables there are in a collection. The following rule will trigger if there is more than zero arguments in the request (ignore the second parameter for the time being):

    SecRule &ARGS !^0$

And sometimes you need to look at an array of parameters, each with a slightly different name. In this case you can specify a regular expression in the selection operator itself. The following rule will look into all arguments whose names begin with `id_`:

    SecRule ARGS:/^id_/ dirty

### Note

Using `ARGS:p` will not result in any invocations against the operator if argument p does not exist.

In ModSecurity 1.X, the `ARGS` variable stood for `QUERY_STRING` + `POST_PAYLOAD`, whereas now it expands to individual variables.

### `ARGS_COMBINED_SIZE`

This variable allows you to set more targeted evaluations on the total size of the Arguments as compared with normal Apache LimitRequest directives. For example, you could create a rule to ensure that the total size of the argument data is below a certain threshold (to help prevent buffer overflow issues). Example: Block request if the size of the arguments is above 25 characters.

    SecRule REQUEST_FILENAME "^/cgi-bin/login\.php" \
        "chain,log,deny,phase:2,t:none,t:lowercase,t:normalisePath"
    SecRule ARGS_COMBINED_SIZE "@gt 25"

### `ARGS_NAMES`

Is a collection of the argument names. You can search for specific argument names that you want to block. In a positive policy scenario, you can also whitelist (using an inverted rule with the ! character) only authorized argument names. Example: This example rule will only allow 2 argument names - p and a. If any other argument names are injected, it will be blocked.

    SecRule REQUEST_FILENAME "/index.php" \
        "chain,log,deny,status:403,phase:2,t:none,t:lowercase,t:normalisePath"
    SecRule ARGS_NAMES "!^(p|a)$" "t:none,t:lowercase"

### `ARGS_GET`

`ARGS_GET` is similar to `ARGS`, but only contains arguments from the query string.

### `ARGS_GET_NAMES`

`ARGS_GET_NAMES` is similar to `ARGS_NAMES`, but only contains argument names from the query string.

### `ARGS_POST`

`ARGS_POST` is similar to `ARGS`, but only contains arguments from the POST body.

### `ARGS_POST_NAMES`

`ARGS_POST_NAMES` is similar to `ARGS_NAMES`, but only contains argument names from the POST body.

### `AUTH_TYPE`

This variable holds the authentication method used to validate a user. Example:

    SecRule AUTH_TYPE "basic" log,deny,status:403,phase:1,t:lowercase

Note

This data will not be available in a proxy-mode deployment as the authentication is not local. In a proxy-mode deployment, you would need to inspect the `REQUEST_HEADERS:Authorization` header.

### `ENV`

Collection, requires a single parameter (after colon). The `ENV` variable is set with setenv and does not give access to the CGI environment variables. Example:

    SecRule REQUEST_FILENAME "printenv" pass,setenv:tag=suspicious
    SecRule ENV:tag "suspicious"

### `FILES`

Collection. Contains a collection of original file names (as they were called on the remote user's file system). Note: only available if files were extracted from the request body. Example:

    SecRule FILES "\.conf$" log,deny,status:403,phase:2

### `FILES_COMBINED_SIZE`

Single value. Total size of the uploaded files. Note: only available if files were extracted from the request body. Example:

    SecRule FILES_COMBINED_SIZE "@gt 1000" log,deny,status:403,phase:2

### `FILES_NAMES`

Collection w/o parameter. Contains a list of form fields that were used for file upload. Note: only available if files were extracted from the request body. Example:

    SecRule FILES_NAMES "^upfile$" log,deny,status:403,phase:2

### `FILES_SIZES`

Collection. Contains a list of file sizes. Useful for implementing a size limitation on individual uploaded files. Note: only available if files were extracted from the request body. Example:

    SecRule FILES_SIZES "@gt 100" log,deny,status:403,phase:2

### `FILES_TMPNAMES`

Collection. Contains a collection of temporary files' names on the disk. Useful when used together with `@inspectFile.` Note: only available if files were extracted from the request body. Example:

    SecRule FILES_TMPNAMES "@inspectFile /path/to/inspect_script.pl"

### `GEO`

`GEO` is a collection populated by the `@geoLookups` operator. It can be used to match geographical fields looked up by an IP address or hostname.

Available since 2.2.0.

Fields:

- COUNTRY_CODE: Two character country code. EX: US, UK, etc.

- COUNTRY_CODE3: Up to three character country code.

- COUNTRY_NAME: The full country name.

- COUNTRY_CONTINENT: The two character continent that the country is located. EX: EU

- REGION: The two character region. For US, this is state. For Canada, providence, etc.

- CITY: The city name.

- POSTAL_CODE: The postal code.

- LATITUDE: The latitude.

- LONGITUDE: The longitude.

- DMA_CODE: The metropolitan area code. (US only)

- AREA_CODE: The phone system area code. (US only)

Example:

    SecRule REMOTE_ADDR "@geoLookup" "chain,drop,msg:'Non-UK IP address'"
    SecRule GEO:COUNTRY_CODE "!@streq UK"

### `HIGHEST_SEVERITY`

This variable holds the highest severity of any rules that have matched so far. Severities are numeric values and thus can be used with comparison operators such as `@lt`, etc.

### Note

Higher severities have a lower numeric value.

A value of 255 indicates no severity has been set.

    SecRule HIGHEST_SEVERITY "@le 2" "phase:2,deny,status:500,msg:'severity %{HIGHEST_SEVERITY}'"

### `MATCHED_VAR`

This variable holds the value of the variable that was matched against. It is similar to the TX:0, except it can be used for all operators and does not require that the `capture` action be specified.

    SecRule ARGS pattern chain,deny
    ...
    SecRule MATCHED_VAR "further scrutiny"

### `MATCHED_VAR_NAME`

This variable holds the full name of the variable that was matched against.

    SecRule ARGS pattern setvar:tx.mymatch=%{MATCHED_VAR_NAME}
    ...
    SecRule TX:MYMATCH "@eq ARGS:param" deny

### `MODSEC_BUILD`

This variable holds the ModSecurity build number. This variable is intended to be used to check the build number prior to using a feature that is available only in a certain build. Example:

    SecRule MODSEC_BUILD "!@ge 02050102" skipAfter:12345
    SecRule ARGS "@pm some key words" id:12345,deny,status:500

### `MULTIPART_CRLF_LF_LINES`

This flag variable will be set to `1` whenever a multi-part request uses mixed line terminators. The `multipart/form-data` RFC requires `CRLF` sequence to be used to terminate lines. Since some client implementations use only `LF` to terminate lines you might want to allow them to proceed under certain circumstances (if you want to do this you will need to stop using `MULTIPART_STRICT_ERROR` and check each multi-part flag variable individually, avoiding `MULTIPART_LF_LINE`). However, mixing `CRLF` and `LF` line terminators is dangerous as it can allow for evasion. Therefore, in such cases, you will have to add a check for `MULTIPART_CRLF_LF_LINES`.

### `MULTIPART_STRICT_ERROR`

`MULTIPART_STRICT_ERROR` will be set to `1` when any of the following variables is also set to `1`: `REQBODY_PROCESSOR_ERROR`, `MULTIPART_BOUNDARY_QUOTED`, `MULTIPART_BOUNDARY_WHITESPACE`, `MULTIPART_DATA_BEFORE`, `MULTIPART_DATA_AFTER`, `MULTIPART_HEADER_FOLDING`, `MULTIPART_LF_LINE`, `MULTIPART_SEMICOLON_MISSING`. Each of these variables covers one unusual (although sometimes legal) aspect of the request body in `multipart/form-data format`. Your policies should always contain a rule to check either this variable (easier) or one or more individual variables (if you know exactly what you want to accomplish). Depending on the rate of false positives and your default policy you should decide whether to block or just warn when the rule is triggered.

The best way to use this variable is as in the example below:

    SecRule MULTIPART_STRICT_ERROR "!@eq 0" \
    "phase:2,t:none,log,deny,msg:'Multipart request body \
    failed strict validation: \
    PE %{REQBODY_PROCESSOR_ERROR}, \
    BQ %{MULTIPART_BOUNDARY_QUOTED}, \
    BW %{MULTIPART_BOUNDARY_WHITESPACE}, \
    DB %{MULTIPART_DATA_BEFORE}, \
    DA %{MULTIPART_DATA_AFTER}, \
    HF %{MULTIPART_HEADER_FOLDING}, \
    LF %{MULTIPART_LF_LINE}, \
    SM %{MULTIPART_SEMICOLON_MISSING}'"

The `multipart/form-data` parser was upgraded in ModSecurity v2.1.3 to actively look for signs of evasion. Many variables (as listed above) were added to expose various facts discovered during the parsing process. The `MULTIPART_STRICT_ERROR` variable is handy to check on all abnormalities at once. The individual variables allow detection to be fine-tuned according to your circumstances in order to reduce the number of false positives. Detailed analysis of various evasion techniques covered will be released as a separated document at a later date.

### `MULTIPART_UNMATCHED_BOUNDARY`

Set to `1` when, during the parsing phase of a `multipart/request-body`, ModSecurity encounters what feels like a boundary but it is not. Such an event may occur when evasion of ModSecurity is attempted.

The best way to use this variable is as in the example below:

    SecRule MULTIPART_UNMATCHED_BOUNDARY "!@eq 0" \
    "phase:2,t:none,log,deny,msg:'Multipart parser detected a possible unmatched boundary.'"

Change the rule from blocking to logging-only if many false positives are encountered.

### `PATH_INFO`

Besides passing query information to a script/handler, you can also pass additional data, known as extra path information, as part of the URL. Example:

    SecRule PATH_INFO "^/(bin|etc|sbin|opt|usr)"

### `QUERY_STRING`

This variable holds form data passed to the script/handler by appending data after a question mark. Warning: Not URL-decoded. Example:

    SecRule QUERY_STRING "attack"

### `REMOTE_ADDR`

This variable holds the IP address of the remote client. Example:

    SecRule REMOTE_ADDR "^192\.168\.1\.101$"

### `REMOTE_HOST`

If HostnameLookUps are set to On, then this variable will hold the DNS resolved remote host name. If it is set to Off, then it will hold the remote IP address. Possible uses for this variable would be to deny known bad client hosts or network blocks, or conversely, to allow in authorized hosts. Example:

    SecRule REMOTE_HOST "\.evil\.network\org$"

### `REMOTE_PORT`

This variable holds information on the source port that the client used when initiating the connection to our web server. Example: in this example, we are evaluating to see if the `REMOTE_PORT` is less than 1024, which would indicate that the user is a privileged user (root).

    SecRule REMOTE_PORT "@lt 1024" phase:1,log,pass,setenv:remote_port=privileged

### `REMOTE_USER`

This variable holds the username of the authenticated user. If there are no password (basic|digest) access controls in place, then this variable will be empty. Example:

    SecRule REMOTE_USER "admin"

Note

This data will not be available in a proxy-mode deployment as the authentication is not local.

### `REQBODY_PROCESSOR`

Built-in processors are `URLENCODED`,`MULTIPART`, and `XML`. Example:

    SecRule REQBODY_PROCESSOR "^XML$ chain
    SecRule XML "@validateDTD /opt/apache-frontend/conf/xml.dtd"

### `REQBODY_PROCESSOR_ERROR`

Possible values are 0 (no error) or 1 (error). This variable will be set by request body processors (typically the `multipart/request-data` parser or the XML parser) when they fail to properly parse a request payload.

Example:

    SecRule REQBODY_PROCESSOR_ERROR "@eq 1" deny,phase:2

### Note

Your policies must have a rule to check REQBODY_PROCESSOR_ERROR at the beginning of phase 2. Failure to do so will leave the door open for impedance mismatch attacks. It is possible, for example, that a payload that cannot be parsed by ModSecurity can be successfully parsed by more tolerant parser operating in the application. If your policy dictates blocking then you should reject the request if error is detected. When operating in detection-only mode your rule should alert with high severity when request body processing fails.

### `REQBODY_PROCESSOR_ERROR_MSG`

Empty, or contains the error message from the processor. Example:

    SecRule REQBODY_PROCESSOR_ERROR_MSG "failed to parse" t:lowercase

### `REQUEST_BASENAME`

This variable holds just the filename part of `REQUEST_FILENAME` (e.g. index.php).

Example:

    SecRule REQUEST_BASENAME "^login\.php$" phase:2,t:none,t:lowercase

### Note

Please note that anti-evasion transformations are not applied to this variable by default. `REQUEST_BASENAME` will recognise both `/` and `\` as path separators.

### `REQUEST_BODY`

This variable holds the data in the request body (including `POST_PAYLOAD` data). `REQUEST_BODY` should be used if the original order of the arguments is important (`ARGS` should be used in all other cases). Example:

    SecRule REQUEST_BODY "^username=\w{25,}\&password=\w{25,}\&Submit\=login$"

### Note

This variable is only available if the `URLENCODED` request body processor parsed a request body. This will occur by default when an `application/x-www-form-urlencoded` is detected, or the `URLENCODED` request body parser is forced. As of 2.5.7 it is possible to force the presence of the `REQUEST_BODY` variable, but only when there is no request body processor defined, using the `ctl:forceRequestBodyVariable` option in the `REQUEST_HEADERS` phase.

### `REQUEST_COOKIES`

This variable is a collection of all of the cookie data. Example: the following example is using the Ampersand special operator to count how many variables are in the collection. In this rule, it would trigger if the request does not include any Cookie headers.

    SecRule &REQUEST_COOKIES "@eq 0"

### `REQUEST_COOKIES_NAMES`

This variable is a collection of the cookie names in the request headers. Example: the following rule will trigger if the JSESSIONID cookie is not present.

    SecRule &REQUEST_COOKIES_NAMES:JSESSIONID "@eq 0"

### `REQUEST_FILENAME`

This variable holds the relative `REQUEST_URI` minus the `QUERY_STRING` part (e.g. /index.php). Example:

    SecRule REQUEST_FILENAME "^/cgi-bin/login\.php$" phase:2,t:none,t:normalisePath

### Note

Please note that anti-evasion transformations are not used on `REQUEST_FILENAME` by default.

### `REQUEST_HEADERS`

This variable can be used as either a collection of all of the request headers or can be used to specify individual headers (by using REQUEST_HEADERS:Header-Name). Example: the first example uses `REQUEST_HEADERS` as a collection and is applying the `validateUrlEncoding` operator against all headers.

    SecRule REQUEST_HEADERS "@validateUrlEncoding"

Example: the second example is targeting only the `Host` header.

    SecRule REQUEST_HEADERS:Host "^[\d\.]+$" \
        "deny,log,status:400,msg:'Host header is a numeric IP address'"

### `REQUEST_HEADERS_NAMES`

This variable is a collection of the names of all of the request headers. Example:

    SecRule REQUEST_HEADERS_NAMES "^x-forwarded-for" \
        "log,deny,status:403,t:lowercase,msg:'Proxy Server Used'"

### `REQUEST_LINE`

This variable holds the complete request line sent to the server (including the REQUEST_METHOD and HTTP version data). Example: this example rule will trigger if the request method is something other than GET, HEAD, POST or if the HTTP is something other than HTTP/0.9, 1.0 or 1.1.

    SecRule REQUEST_LINE "!(^((?:(?:pos|ge)t|head))|http/(0\.9|1\.0|1\.1)$)" t:none,t:lowercase

### `REQUEST_METHOD`

This variable holds the request method used by the client.

The following example will trigger if the request method is either `CONNECT` or TRACE.

    SecRule REQUEST_METHOD "^((?:connect|trace))$" t:none,t:lowercase

### `REQUEST_PROTOCOL`

This variable holds the request protocol version information. Example:

    SecRule REQUEST_PROTOCOL "!^http/(0\.9|1\.0|1\.1)$" t:none,t:lowercase

### `REQUEST_URI`

This variable holds the full URL including the `QUERY_STRING` data (e.g. /index.php?p=X), however it will never contain a domain name, even if it was provided on the request line. It also does not include either the `REQUEST_METHOD` or the HTTP version info.

Example:

    SecRule REQUEST_URI "attack" phase:1,t:none,t:urlDecode,t:lowercase,t:normalisePath

### Note

Please note that anti-evasion transformations are not used on `REQUEST_URI` by default.

### `REQUEST_URI_RAW`

Same as `REQUEST_URI` but will contain the domain name if it was provided on the request line (e.g. http://www.example.com/index.php?p=X).

Example:

    SecRule REQUEST_URI_RAW "http:/" phase:1,t:none,t:urlDecode,t:lowercase,t:normalisePath

### Note

Please note that anti-evasion transformations are not used on `REQUEST_URI_RAW` by default.

### `RESPONSE_BODY`

This variable holds the data for the response payload.

Example:

    SecRule RESPONSE_BODY "ODBC Error Code"

### `RESPONSE_CONTENT_LENGTH`

Response body length in bytes. Can be available starting with phase 3 but it does not have to be (as the length of response body is not always known in advance.) If the size is not known this variable will contain a zero. If `RESPONSE_CONTENT_LENGTH` contains a zero in phase 5 that means the actual size of the response body was 0.

The value of this variable can change between phases if the body is modified. For example, in embedded mode `mod_deflate` can compress the response body between phases 4 and 5.

### `RESPONSE_CONTENT_TYPE`

Response content type. Only available starting with phase 3.

### `RESPONSE_HEADERS`

This variable is similar to the REQUEST_HEADERS variable and can be used in the same manner. Example:

    SecRule RESPONSE_HEADERS:X-Cache "MISS"

Note

This variable may not have access to some headers when running in embedded-mode. Headers such as Server, Date, Connection and Content-Type are added during a later Apache hook just prior to sending the data to the client. This data should be available, however, either during ModSecurity phase:5 (logging) or when running in proxy-mode.

### `RESPONSE_HEADERS_NAMES`

This variable is a collection of the response header names. Example:

    SecRule RESPONSE_HEADERS_NAMES "Set-Cookie"

Note

Same limitations as RESPONSE_HEADERS with regards to access to some headers in embedded-mode.

### `RESPONSE_PROTOCOL`

This variable holds the HTTP response protocol information. Example:

    SecRule RESPONSE_PROTOCOL "^HTTP\/0\.9"

### `RESPONSE_STATUS`

This variable holds the HTTP response status code as generated by Apache. Example:

    SecRule RESPONSE_STATUS "^[45]"

Note

This directive may not work as expected in embedded-mode as Apache handles many of the stock response codes (404, 401, etc...) earlier in Phase 2. This variable should work as expected in a proxy-mode deployment.

### `RULE`

This variable provides access to the `id`, `rev`, `severity`, `logdata`, and `msg` fields of the rule that triggered the action. Only available for expansion in action strings (e.g.`setvar:tx.varname=%{rule.id}`). Example:

    SecRule &REQUEST_HEADERS:Host "@eq 0" "log,deny,setvar:tx.varname=%{rule.id}"

### `SCRIPT_BASENAME`

This variable holds just the local filename part of SCRIPT_FILENAME. Example:

    SecRule SCRIPT_BASENAME "^login\.php$"

Note

This variable is not available in proxy mode.

### `SCRIPT_FILENAME`

This variable holds the full path on the server to the requested script. (e.g. SCRIPT_NAME plus the server path). Example:

    SecRule SCRIPT_FILENAME "^/usr/local/apache/cgi-bin/login\.php$"

Note

This variable is not available in proxy mode.

### `SCRIPT_GID`

This variable holds the group id (numerical value) of the group owner of the script. Example:

    SecRule SCRIPT_GID "!^46$"

Note

This variable is not available in proxy mode.

### `SCRIPT_GROUPNAME`

This variable holds the group name of the group owner of the script. Example:

    SecRule SCRIPT_GROUPNAME "!^apache$"

Note

This variable is not available in proxy mode.

### `SCRIPT_MODE`

This variable holds the script's permissions mode data (numerical - 1=execute, 2=write, 4=read and 7=read/write/execute). Example: will trigger if the script has the WRITE permissions set.

    SecRule SCRIPT_MODE "^(2|3|6|7)$"

Note

This variable is not available in proxy mode.

### `SCRIPT_UID`

This variable holds the user id (numerical value) of the owner of the script. Example: the example rule below will trigger if the UID is not 46 (the Apache user).

    SecRule SCRIPT_UID "!^46$"

Note

This variable is not available in proxy mode.

### `SCRIPT_USERNAME`

This variable holds the username of the owner of the script. Example:

    SecRule SCRIPT_USERNAME "!^apache$"

Note

This variable is not available in proxy mode.

### `SERVER_ADDR`

This variable contains the IP address of the server. Example:

    SecRule SERVER_ADDR "^192\.168\.1\.100$"

### `SERVER_NAME`

This variable contains the server's hostname or IP address. Example:

    SecRule SERVER_NAME "hostname\.com$"

Note

This data is taken from the Host header submitted in the client request.

### `SERVER_PORT`

This variable contains the local port that the web server is listening on. Example:

    SecRule SERVER_PORT "^80$"

### `SESSION`

This variable is a collection, available only after `setsid` is executed. Example: the following example shows how to initialize a SESSION collection with setsid, how to use setvar to increase the session.score values, how to set the session.blocked variable and finally how to deny the connection based on the session:blocked value.

    SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass
    SecAction setsid:%{REQUEST_COOKIES.PHPSESSID}
    SecRule REQUEST_URI "^/cgi-bin/finger$" \
        "phase:2,t:none,t:lowercase,t:normalisePath,pass,log,setvar:session.score=+10"
    SecRule SESSION:SCORE "@gt 50" "pass,log,setvar:session.blocked=1"
    SecRule SESSION:BLOCKED "@eq 1" "log,deny,status:403"

### `SESSIONID`

This variable is the value set with `setsid`. Example:

    SecRule SESSIONID !^$ chain,nolog,pass
    SecRule REQUEST_COOKIES:PHPSESSID !^$
    SecAction setsid:%{REQUEST_COOKIES.PHPSESSID}

### `TIME`

This variable holds a formatted string representing the time (hour:minute:second). Example:

    SecRule TIME "^(([1](8|9))|([2](0|1|2|3))):\d{2}:\d{2}$"

### `TIME_DAY`

This variable holds the current date (1-31). Example: this rule would trigger anytime between the 10th and 20th days of the month.

    SecRule TIME_DAY "^(([1](0|1|2|3|4|5|6|7|8|9))|20)$"

### `TIME_EPOCH`

This variable holds the time in seconds since 1970. Example:

    SecRule TIME_EPOCH "@gt 1000"

### `TIME_HOUR`

This variable holds the current hour (0-23). Example: this rule would trigger during "off hours".

    SecRule TIME_HOUR "^(0|1|2|3|4|5|6|[1](8|9)|[2](0|1|2|3))$"

### `TIME_MIN`

This variable holds the current minute (0-59). Example: this rule would trigger during the last half hour of every hour.

    SecRule TIME_MIN "^(3|4|5)"

### `TIME_MON`

This variable holds the current month (0-11). Example: this rule would match if the month was either November (10) or December (11).

    SecRule TIME_MON "^1"

### `TIME_SEC`

This variable holds the current second count (0-59). Example:

    SecRule TIME_SEC "@gt 30"

### `TIME_WDAY`

This variable holds the current weekday (0-6). Example: this rule would trigger only on week-ends (Saturday and Sunday).

    SecRule TIME_WDAY "^(0|6)$"

### `TIME_YEAR`

This variable holds the current four-digit year data. Example:

    SecRule TIME_YEAR "^2006$"

### `TX`

Transaction Collection. This is used to store pieces of data, create a transaction anomaly score, and so on. Transaction variables are set for 1 request/response cycle. The scoring and evaluation will not last past the current request/response process. Example: In this example, we are using setvar to increase the tx.score value by 5 points. We then have a follow-up run that will evaluate the transactional score this request and then it will decided whether or not to allow/deny the request through.

The following is a list of reserved names in the TX collection:

- `TX:0` - The matching value when using the `@rx` or `@pm` operator with the `capture` action.

- `TX:1-TX:9` - The captured subexpression value when using the `@rx` operator with capturing parens and the `capture` action.

    SecRule WEBSERVER_ERROR_LOG "does not exist" "phase:5,pass,setvar:tx.score=+5"
    SecRule TX:SCORE "@gt 20" deny,log

### `USERID`

This variable is the value set with `setuid`. Example:

    SecAction setuid:%{REMOTE_USER},nolog
    SecRule USERID "Admin"

### `WEBAPPID`

This variable is the value set with `SecWebAppId`. Example:

    SecWebAppId "WebApp1"
    SecRule WEBAPPID "WebApp1" "chain,log,deny,status:403"
    SecRule REQUEST_HEADERS:Transfer-Encoding "!^$"

### `WEBSERVER_ERROR_LOG`

Contains zero or more error messages produced by the web server. Access to this variable is in phase:5 (logging). Example:

    SecRule WEBSERVER_ERROR_LOG "File does not exist" "phase:5,setvar:tx.score=+5"

### `XML`

Can be used standalone (as a target for `validateDTD` and `validateSchema`) or with an XPath expression parameter (which makes it a valid target for any function that accepts plain text). Example using XPath:

    SecDefaultAction log,deny,status:403,phase:2
    SecRule REQUEST_HEADERS:Content-Type ^text/xml$ \
        phase:1,t:lowercase,nolog,pass,ctl:requestBodyProcessor=XML
    SecRule REQBODY_PROCESSOR "!^XML$" skipAfter:12345
    SecRule XML:/employees/employee/name/text() Fred
    SecRule XML:/xq:employees/employee/name/text() Fred \
        id:12345,xmlns:xq=http://www.example.com/employees

The first XPath expression does not use namespaces. It would match against payload such as this one:

    <employees>
        <employee>
            <name>Fred Jones</name>
            <address location="home">
                <street>900 Aurora Ave.</street>
                <city>Seattle</city>
                <state>WA</state>
                <zip>98115</zip>
            </address>
            <address location="work">
                <street>2011 152nd Avenue NE</street>
                <city>Redmond</city>
                <state>WA</state>
                <zip>98052</zip>
            </address>
            <phone location="work">(425)555-5665</phone>
            <phone location="home">(206)555-5555</phone>
            <phone location="mobile">(206)555-4321</phone>
        </employee>
    </employees>

The second XPath expression does use namespaces. It would match the following payload:

    <xq:employees xmlns:xq="http://www.example.com/employees">
        <employee>
            <name>Fred Jones</name>
            <address location="home">
                <street>900 Aurora Ave.</street>
                <city>Seattle</city>
                <state>WA</state>
                <zip>98115</zip>
            </address>
            <address location="work">
                <street>2011 152nd Avenue NE</street>
                <city>Redmond</city>
                <state>WA</state>
                <zip>98052</zip>
            </address>
            <phone location="work">(425)555-5665</phone>
            <phone location="home">(206)555-5555</phone>
            <phone location="mobile">(206)555-4321</phone>
        </employee>
    </xq:employees>

Note the different namespace used in the second example.

To learn more about XPath we suggest the following resources:

1. XPath Standard

2. XPath Tutorial

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