Description: Stops rule processing on a successful match and allows the transaction to proceed.

Action Group: Disruptive

Example:

SecRule REMOTE_ADDR "^192\.168\.1\.100$" nolog,phase:1,allow

Prior to ModSecurity 2.5 the allow action would only affect the current phase. An allow in phase 1 would skip processing the remaining rules in phase 1 but the rules from phase 2 would execute. Starting with v2.5.0 allow was enhanced to allow for fine-grained control of what is done. The following rules now apply:

Examples:

# Do not process request but process response.
SecAction phase:1,allow:request

# Do not process transaction (request and response).
SecAction phase:1,allow

If you want to allow a response through, put a rule in phase RESPONSE_HEADERS and simply use allow on its own:

# Allow response through.
SecAction phase:3,allow

Description: Appends text given as parameter to the end of response body. For this action to work content injection must be enabled by setting SecContentInjection to On. Also make sure you check the content type of the response before you make changes to it (e.g. you don't want to inject stuff into images).

Action Group: Non-disruptive

Processing Phases: 3 and 4.

Example:

SecRule RESPONSE_CONTENT_TYPE "^text/html" "nolog,pass,append:'<hr>Footer'"

Description: Marks the transaction for logging in the audit log.

Action Group: Non-disruptive

Example:

SecRule REMOTE_ADDR "^192\.168\.1\.100$" auditlog,phase:1,allow

Note

The auditlog action is now explicit if log is already specified.

Description: Performs the default disruptive action.

Action Group: Disruptive

It is intended to be used by ruleset writers to signify that the rule was intended to block and leaves the "how" up to the administrator. This action is currently a placeholder which will just be replaced by the action from the last SecDefaultAction in the same context. Using the block action with the SecRuleUpdateActionById directive allows a rule to be reverted back to the previous SecDefaultAction disruptive action.

In future versions of ModSecurity, more control and functionality will be added to define "how" to block.

Examples:

In the following example, the second rule will "deny" because of the SecDefaultAction disruptive action. The intent being that the administrator could easily change this to another disruptive action without editing the actual rules.

### Administrator defines "how" to block (deny,status:403)...
SecDefaultAction phase:2,deny,status:403,log,auditlog

### Included from a rulest...
# Intent is to warn for this User Agent
SecRule REQUEST_HEADERS:User-Agent "perl" "phase:2,pass,msg:'Perl based user agent identified'"
# Intent is to block for this User Agent, "how" described in SecDefaultAction
SecRule REQUEST_HEADERS:User-Agent "nikto" "phase:2,block,msg:'Nikto Scanners Identified'"

In the following example, The rule is reverted back to the pass action defined in the SecDefaultAction directive by using the SecRuleUpdateActionById directive in conjuction with the block action. This allows an administrator to override an action in a 3rd party rule without modifying the rule itself.

### Administrator defines "how" to block (deny,status:403)...
SecDefaultAction phase:2,pass,log,auditlog

### Included from a rulest...
SecRule REQUEST_HEADERS:User-Agent "nikto" "id:1,phase:2,deny,msg:'Nikto Scanners Identified'"

### Added by the administrator
SecRuleUpdateActionById 1 "block"

Description: When used together with the regular expression operator, capture action will create copies of regular expression captures and place them into the transaction variable collection. Up to ten captures will be copied on a successful pattern match, each with a name consisting of a digit from 0 to 9.

Action Group: Non-disruptive

Example:

SecRule REQUEST_BODY "^username=(\w{25,})" phase:2,capture,t:none,chain
SecRule TX:1 "(?:(?:a(dmin|nonymous)))"

Note

The 0 data captures the entire REGEX match and 1 captures the data in the first parens, etc...

Description: Chains the rule where the action is placed with the rule that immediately follows it. The result is called a rule chain. Chained rules allow for more complex rule matches where you want to use a number of different VARIABLES to create a better rule and to help prevent false positives.

Action Group: Flow

Example:

# Refuse to accept POST requests that do
# not specify request body length. Do note that
# this rule should be preceeded by a rule that verifies
# only valid request methods (e.g. GET, HEAD and POST) are used.
SecRule REQUEST_METHOD ^POST$ chain,t:none
SecRule REQUEST_HEADERS:Content-Length ^$ t:none

Description: The ctl action allows configuration options to be updated for the transaction.

Action Group: Non-disruptive

Example:

# Parse requests with Content-Type "text/xml" as XML 
SecRule REQUEST_CONTENT_TYPE ^text/xml nolog,pass,ctl:requestBodyProcessor=XML

Note

The following configuration options are supported:

With the exception of requestBodyProcessor and forceRequestBodyVariable, each configuration option corresponds to one configuration directive and the usage is identical.

The requestBodyProcessor option allows you to configure the request body processor. By default ModSecurity will use the URLENCODED and MULTIPART processors to process an application/x-www-form-urlencoded and a multipart/form-data bodies, respectively. A third processor, XML, is also supported, but it is never used implicitly. Instead you must tell ModSecurity to use it by placing a few rules in the REQUEST_HEADERS processing phase. After the request body was processed as XML you will be able to use the XML-related features to inspect it.

Request body processors will not interrupt a transaction if an error occurs during parsing. Instead they will set variables REQBODY_PROCESSOR_ERROR and REQBODY_PROCESSOR_ERROR_MSG. These variables should be inspected in the REQUEST_BODY phase and an appropriate action taken.

The forceRequestBodyVariable option allows you to configure the REQUEST_BODY variable to be set when there is no request body processor configured. This allows for inspection of request bodies of unknown types.

Description: Stops rule processing and intercepts transaction.

Action Group: Disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "nikto" "log,deny,msg:'Nikto Scanners Identified'"

Description: Decrement counter based on its age.

Action Group: Non-Disruptive

Example: The following example will decrement the counter by 60 every 300 seconds.

SecAction deprecatevar:session.score=60/300

Note

Counter values are always positive, meaning the value will never go below zero.

Description: Immediately initiate a "connection close" action to tear down the TCP connection by sending a FIN packet.

Action Group: Disruptive

Example: The following example initiates an IP collection for tracking Basic Authentication attempts. If the client goes over the threshold of more than 25 attempts in 2 minutes, it will DROP subsequent connections.

SecAction phase:1,initcol:ip=%{REMOTE_ADDR},nolog
SecRule ARGS:login "!^$" \
    nolog,phase:1,setvar:ip.auth_attempt=+1,deprecatevar:ip.auth_attempt=20/120
SecRule IP:AUTH_ATTEMPT "@gt 25" \
    "log,drop,phase:1,msg:'Possible Brute Force Attack'"

Note

This action is currently not available on Windows based builds. This action is extremely useful when responding to both Brute Force and Denial of Service attacks in that, in both cases, you want to minimize both the network bandwidth and the data returned to the client. This action causes error message to appear in the log "(9)Bad file descriptor: core_output_filter: writing data to the network"

Description: Executes an external script/binary supplied as parameter. As of v2.5.0, if the parameter supplied to exec is a Lua script (detected by the .lua extension) the script will be processed internally. This means you will get direct access to the internal request context from the script. Please read the SecRuleScript documentation for more details on how to write Lua scripts.

Action Group: Non-disruptive

Example:

# The following is going to execute /usr/local/apache/bin/test.sh
# as a shell script on rule match.
SecRule REQUEST_URI "^/cgi-bin/script\.pl" \
    "phase:2,t:none,t:lowercase,t:normalisePath,log,exec:/usr/local/apache/bin/test.sh"

# The following is going to process /usr/local/apache/conf/exec.lua
# internally as a Lua script on rule match.
SecRule ARGS:p attack log,exec:/usr/local/apache/conf/exec.lua

Description: Configures a collection variable to expire after the given time in seconds.

Action Group: Non-disruptive

Example:

SecRule REQUEST_COOKIES:JSESSIONID "!^$" nolog,phase:1,pass,chain
SecAction setsid:%{REQUEST_COOKIES:JSESSIONID}
SecRule REQUEST_URI "^/cgi-bin/script\.pl" \
    "phase:2,t:none,t:lowercase,t:normalisePath,log,allow,\
setvar:session.suspicious=1,expirevar:session.suspicious=3600,phase:1"

Note

You should use expirevar actions at the same time that you use setvar actions in order to keep the indented expiration time. If they are used on their own (perhaps in a SecAction directive) the expire time could get re-set. When variables are removed from collections, and there are no other changes, collections are not written to disk at the end of request. This is because the variables can always be expired again when the collection is read again on a subsequent request.

Description: Assigns a unique ID to the rule or chain.

Action Group: Meta-data

Example:

SecRule &REQUEST_HEADERS:Host "@eq 0" \
    "log,id:60008,severity:2,msg:'Request Missing a Host Header'"

Note

These are the reserved ranges:

Description: Initialises a named persistent collection, either by loading data from storage or by creating a new collection in memory.

Action Group: Non-disruptive

Example: The following example initiates IP address tracking.

SecAction phase:1,initcol:ip=%{REMOTE_ADDR},nolog

Note

Normally you will want to use phase:1 along with initcol so that the collection is available in all phases.

Collections are loaded into memory when the initcol action is encountered. The collection in storage will be persisted (and the appropriate counters increased) only if it was changed during transaction processing.

See the "Persistant Storage" section for further details.

Description: Indicates that a successful match of the rule needs to be logged.

Action Group: Non-disruptive

Example:

SecAction phase:1,initcol:ip=%{REMOTE_ADDR},log

Note

This action will log matches to the Apache error log file and the ModSecurity audit log.

Description: Allows a data fragment to be logged as part of the alert message.

Action Group: Non-disruptive

Example:

SecRule &ARGS:p "@eq 0" "log,logdata:'%{TX.0}'"

Note

The logdata information appears in the error and/or audit log files and is not sent back to the client in response headers. Macro expansion is preformed so you may use variable names such as %{TX.0}, etc. The information is properly escaped for use with logging binary data.

Description: Assigns a custom message to the rule or chain.

Action Group: Meta-data

Example:

SecRule &REQUEST_HEADERS:Host "@eq 0" \
    "log,id:60008,severity:2,msg:'Request Missing a Host Header'"

Note

The msg information appears in the error and/or audit log files and is not sent back to the client in response headers.

Description: If enabled ModSecurity will perform multiple operator invocations for every target, before and after every anti-evasion transformation is performed.

Action Group: Non-disruptive

Example:

SecDefaultAction log,deny,phase:1,t:removeNulls,t:lowercase
SecRule ARGS "attack" multiMatch

Note

Normally, variables are evaluated once, only after all transformation functions have completed. With multiMatch, variables are checked against the operator before and after every transformation function that changes the input.

Description: Indicates that a successful match of the rule should not be used as criteria whether the transaction should be logged to the audit log.

Action Group: Non-disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "Test" allow,noauditlog

Note

If the SecAuditEngine is set to On, all of the transactions will be logged. If it is set to RelevantOnly, then you can control it with the noauditlog action. Even if the noauditlog action is applied to a specific rule and a rule either before or after triggered an audit event, then the transaction will be logged to the audit log. The correct way to disable audit logging for the entire transaction is to use "ctl:auditEngine=Off"

Description: Prevents rule matches from appearing in both the error and audit logs.

Action Group: Non-disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "Test" allow,nolog

Note

The nolog action also implies noauditlog.

Description: Continues processing with the next rule in spite of a successful match.

Action Group: Disruptive

Example1:

SecRule REQUEST_HEADERS:User-Agent "Test" log,pass

When using pass with SecRule with multiple targets, all targets will be processed and all non-disruptive actions will trigger for every match found. In the second example the TX:test target would be incremented by 1 for each matching argument.

Example2:

SecRule ARGS "test" log,pass,setvar:TX.test=+1

Note

The transaction will not be interrupted but a log will be generated for each matching target (unless logging has been suppressed).

Description: Pauses transaction processing for the specified number of milliseconds.

Action Group: Non-disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "Test" log,deny,status:403,pause:5000

Note

This feature can be of limited benefit for slowing down Brute Force Scanners, however use with care. If you are under a Denial of Service type of attack, the pause feature may make matters worse as this feature will cause child processes to sit idle until the pause is completed.

Description: Places the rule (or the rule chain) into one of five available processing phases.

Action Group: Meta-data

Example:

SecDefaultAction log,deny,phase:1,t:removeNulls,t:lowercase
SecRule REQUEST_HEADERS:User-Agent "Test" log,deny,status:403

Note

Keep in mind that is you specify the incorrect phase, the target variable that you specify may be empty. This could lead to a false negative situation where your variable and operator (RegEx) may be correct, but it misses malicious data because you specified the wrong phase.

Description: Prepends text given as parameter to the response body. For this action to work content injection must be enabled by setting SecContentInjection to On. Also make sure you check the content type of the response before you make changes to it (e.g. you don't want to inject stuff into images).

Action Group: Non-disruptive

Processing Phases: 3 and 4.

Example:

SecRule RESPONSE_CONTENT_TYPE ^text/html "phase:3,nolog,pass,prepend:'Header<br>'"

Description: Intercepts transaction by forwarding request to another web server using the proxy backend.

Action Group: Disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "Test" log,proxy:http://www.honeypothost.com/

Note

For this action to work, mod_proxy must also be installed. This action is useful if you would like to proxy matching requests onto a honeypot webserver.

Description: Intercepts transaction by issuing a redirect to the given location.

Action Group: Disruptive

Example:

SecRule REQUEST_HEADERS:User-Agent "Test" \
    log,redirect:http://www.hostname.com/failed.html

Note

If the status action is present and its value is acceptable (301, 302, 303, or 307) it will be used for the redirection. Otherwise status code 302 will be used.

Description: Specifies rule revision.

Action Group: Meta-data

Example:

SecRule REQUEST_METHOD "^PUT$" "id:340002,rev:1,severity:2,msg:'Restricted HTTP function'"

Note

This action is used in combination with the id action to allow the same rule ID to be used after changes take place but to still provide some indication the rule changed.

Description: Sanitises (replaces each byte with an asterisk) a named request argument prior to audit logging.

Action Group: Non-disruptive

Example:

SecAction nolog,phase:2,sanitiseArg:password

Note

The sanitize actions do not sanitize any data within the actual raw requests but only on the copy of data within memory that is set to log to the audit log. It will not sanitize the data in the modsec_debug.log file (if the log level is set high enough to capture this data).

Description: Sanitises the variable (request argument, request header, or response header) that caused a rule match.

Action Group: Non-disruptive

Example: This action can be used to sanitise arbitrary transaction elements when they match a condition. For example, the example below will sanitise any argument that contains the word password in the name.

SecRule ARGS_NAMES password nolog,pass,sanitiseMatched

Note

Same note as sanitiseArg.

Description: Sanitises a named request header.

Action Group: Non-disruptive

Example: This will sanitise the data in the Authorization header.

SecAction log,phase:1,sanitiseRequestHeader:Authorization

Note

Same note as sanitiseArg.

Description: Sanitises a named response header.

Action Group: Non-disruptive

Example: This will sanitise the Set-Cookie data sent to the client.

SecAction log,phase:3,sanitiseResponseHeader:Set-Cookie

Note

Same note as sanitiseArg.

Description: Assigns severity to the rule it is placed with.

Action Group: Meta-data

Example:

SecRule REQUEST_METHOD "^PUT$" "id:340002,rev:1,severity:CRITICAL,msg:'Restricted HTTP function'"

Note

Severity values in ModSecurity follow those of syslog, as below:

It is possible to specify severity levels using either the numerical values or the text values. You should always specify severity levels using the text values. The use of the numerical values is deprecated (as of v2.5.0) and may be removed in one of the susequent major updates.

Description: Special-purpose action that initialises the USER collection.

Action Group: Non-disruptive

Example:

SecAction setuid:%{REMOTE_USER},nolog

Note

After initialisation takes place the variable USERID will be available for use in the subsequent rules.

Description: Special-purpose action that initialises the SESSION collection.

Action Group: Non-disruptive

Example:

# Initialise session variables using the session cookie value 
SecRule REQUEST_COOKIES:PHPSESSID !^$ chain,nolog,pass
SecAction setsid:%{REQUEST_COOKIES.PHPSESSID}

Note

On first invocation of this action the collection will be empty (not taking the predefined variables into account - see initcol for more information). On subsequent invocations the contents of the collection (session, in this case) will be retrieved from storage. After initialisation takes place the variable SESSIONID will be available for use in the subsequent rules.This action understands each application maintains its own set of sessions. It will utilise the current web application ID to create a session namespace.

Description: Creates, removes, or updates an environment variable.

Action Group: Non-disruptive

Examples:

To create a new variable (if you omit the value 1 will be used):

setenv:name=value

To remove a variable:

setenv:!name

Note

This action can be used to establish communication with other Apache modules.

Description: Creates, removes, or updates a variable in the specified collection.

Action Group: Non-disruptive

Examples:

To create a new variable:

setvar:tx.score=10

To remove a variable prefix the name with exclamation mark:

setvar:!tx.score

To increase or decrease variable value use + and - characters in front of a numerical value:

setvar:tx.score=+5

Description: Skips one or more rules (or chains) on successful match.

Action Group: Flow

Example:

SecRule REQUEST_URI "^/$" \
"phase:2,chain,t:none,skip:2"
SecRule REMOTE_ADDR "^127\.0\.0\.1$" "chain"
SecRule REQUEST_HEADERS:User-Agent "^Apache \(internal dummy connection\)$" "t:none"  
SecRule &REQUEST_HEADERS:Host "@eq 0" \
    "deny,log,status:400,id:960008,severity:4,msg:'Request Missing a Host Header'"
SecRule &REQUEST_HEADERS:Accept "@eq 0" \
    "log,deny,log,status:400,id:960015,msg:'Request Missing an Accept Header'"

Note

Skip only applies to the current processing phase and not necessarily the order in which the rules appear in the configuration file. If you group rules by processing phases, then skip should work as expected. This action can not be used to skip rules within one chain. Accepts a single parameter denoting the number of rules (or chains) to skip.

Description: Skips rules (or chains) on successful match resuming rule execution after the specified rule ID or marker (see SecMarker) is found.

Action Group: Flow

Example:

SecRule REQUEST_URI "^/$" "chain,t:none,skipAfter:960015"
SecRule REMOTE_ADDR "^127\.0\.0\.1$" "chain"
SecRule REQUEST_HEADERS:User-Agent "^Apache \(internal dummy connection\)$" "t:none"  
SecRule &REQUEST_HEADERS:Host "@eq 0" \
    "deny,log,status:400,id:960008,severity:4,msg:'Request Missing a Host Header'"
SecRule &REQUEST_HEADERS:Accept "@eq 0" \
    "log,deny,log,status:400,id:960015,msg:'Request Missing an Accept Header'"

Note

SkipAfter only applies to the current processing phase and not necessarily the order in which the rules appear in the configuration file. If you group rules by processing phases, then skip should work as expected. This action can not be used to skip rules within one chain. Accepts a single parameter denoting the last rule ID to skip.

Description: Specifies the response status code to use with actions deny and redirect.

Action Group: Data

Example:

SecDefaultAction log,deny,status:403,phase:1

Note

Status actions defined in Apache scope locations (such as Directory, Location, etc...) may be superseded by phase:1 action settings. The Apache ErrorDocument directive will be triggered if present in the configuration. Therefore if you have previously defined a custom error page for a given status then it will be executed and its output presented to the user.

Description: This action can be used which transformation function should be used against the specified variables before they (or the results, rather) are run against the operator specified in the rule.

Action Group: Non-disruptive

Example:

SecDefaultAction log,deny,phase:1,t:removeNulls,t:lowercase 
SecRule REQUEST_COOKIES:SESSIONID "47414e81cbbef3cf8366e84eeacba091" \
    log,deny,status:403,t:md5,t:hexEncode

Note

Any transformation functions that you specify in a SecRule will be in addition to previous ones specified in SecDefaultAction. Use of "t:none" will remove all transformation functions for the specified rule.

Description: Assigns custom text to a rule or chain.

Action Group: Meta-data

Example:

SecRule REQUEST_FILENAME "\b(?:n(?:map|et|c)|w(?:guest|sh)|cmd(?:32)?|telnet|rcmd|ftp)\.exe\b" \
    "t:none,t:lowercase,deny,msg:'System Command Access',id:'950002',\
tag:'WEB_ATTACK/FILE_INJECTION',tag:'OWASP/A2',severity:'2'"

Note

The tag information appears in the error and/or audit log files. Its intent is to be used to automate classification of rules and the alerts generated by rules. Multiple tags can be used per rule/chain.

Description: This action should be used together with an XPath expression to register a namespace.

Action Group: Data

Example:

SecRule REQUEST_HEADERS:Content-Type "text/xml" \
    "phase:1,pass,ctl:requestBodyProcessor=XML,ctl:requestBodyAccess=On, \
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
SecRule XML:/soap:Envelope/soap:Body/q1:getInput/id() "123" phase:2,deny