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). Note: ARGS:p will not result in any invocations against the operator if argument p does not exist. Some variables are actually collections, which are expanded into more variables at runtime. The following example will examine all request arguments:

SecRule ARGS dirty

SecRule ARGS:p dirty

SecRule ARGS|!ARGS:z dirty

SecRule &ARGS !^0$

SecRule ARGS:/^id_/ dirty

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"
SecRule ARGS_COMBINED_SIZE "@gt 25"

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"
SecRule ARGS_NAMES "!^(p|a)$"

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 inpect the REQUEST_HEADERS:Authorization header.

Collection, requires a single parameter (after a colon character). 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"

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

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

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

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

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"

This variable is a special prefix that is followed by a header name and can be used to access any request header. Example:

SecRule HTTP_REFERER "www\.badsite\.com"

Note

This variable is for backward-compatibilty with ModSecurity 1.X rules. It has been superceded by the REQUEST_HEADERS variable (REQUEST_HEADERS:Headername)

This flag variable will be set to 1 whenever a multipart 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 multipart flag variable individually, avoding 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 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 has been 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.

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 wasy 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.

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)"

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"

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

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

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$"

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

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.

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

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

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

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

SecRule REQBODY_PROCESSOR_ERROR_MSG "failed to parse" t:lowercase

This variable holds just the filename part of REQUEST_FILENAME (e.g. index.php). Warning: not urlDecoded. Example:

SecRule REQUEST_BASENAME "^login\.php$"

This variable holds the data in the request body (including POST_PAYLOAD data). REQUEST_BODY should be used if the original order of the arguements 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 content type is application/x-www-form-urlencoded.

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"

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"

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

SecRule REQUEST_FILENAME "^/cgi-bin/login\.php$"

This variable can be used as either a collection of all of the Request Headers or can be used to specify indivudual 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'"

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'"

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)$)"

Note

Due to the default action transformation function lowercase, the regex strings should be in lowercase as well unless the t:none transformation function is specified for this particular rule.

This variable holds the Request Method used by the client. Example: the following example will trigger if the Request Method is either CONNECT or TRACE.

SecRule REQUEST_METHOD "^((?:connect|trace))$"

Note

Due to the default action transformation function lowercase, the regex strings should be in lowercase as well unless the t:none transformation function is specified for this particular rule.

This variable holds the Request Protocol Version information. Example:

SecRule REQUEST_PROTOCOL "!^http/(0\.9|1\.0|1\.1)$"

Note

Due to the default action transformation function lowercase, the regex strings should be in lowercase as well unless the t:none transformation function is specified for this particular rule.

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. Warning: not urlDecoded. It also does not include either the REQUEST_METHOD or the HTTP version info. Example:

SecRule REQUEST_URI "attack"

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). Warning: not urlDecoded. Example:

SecRule REQUEST_URI_RAW "http:/"

This variable holds the data for the response payload. Example:

SecRule RESPONSE_BODY "ODBC Error Code"

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.

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.

This variable holds the HTTP Response Protocol information. Example:

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

This variable holds the HTTP Response Status Code 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.

This variable provides access to the id,rev,severity, 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}"

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.

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.

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

SecRule SCRIPT_GID "!^46$"

Note

This variable is not available in proxy mode.

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.

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.

This variable holds the userid (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.

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.

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

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

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.

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

SecRule SERVER_PORT "^80$"

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$" "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"

This variable is the value set with setsid. Example:

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

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}$"

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)$"

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

SecRule TIME_EPOCH "@gt 1000"

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))$"

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)"

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"

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

SecRule TIME_SEC "@gt 30"

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)$"

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

SecRule TIME_YEAR "^2006$"

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 this request and then it will decided whether or not to allow/deny the request through.

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

This variable is the value set with setuid. Example:

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

This variable is the value set with SecWebAppId. Example:

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

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"

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$" skip:2
SecRule XML:/employees/employee/name/text() Fred
SecRule XML:/xq:employees/employee/name/text() Fred \
    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: