Directives

The following section outlines all of the Coraza directives.

Include #

Description: Include and evaluate a file or file pattern.

Syntax: Include [PATH_TO_CONF_FILES]

Include loads a file or a list of files from the filesystem using golang Glob syntax.

Example:

Include /path/coreruleset/rules/*.conf

Quoting Glob documentation:

The syntax of patterns is the same as in Match. The pattern may describe hierarchical names such as /usr/*/bin/ed (assuming the Separator is ‘/’). Glob ignores file system errors such as I/O errors reading directories. The only possible returned error is ErrBadPattern, when pattern is malformed.

SecAction #

Description: Unconditionally processes the action list it receives as the first and only parameter.

Syntax: SecAction "action1,action2,action3,..."

This directive is commonly used to set variables and initialize persistent collections using the initcol action. The syntax of the parameter is identical to that of the third parameter of SecRule.

Example:

SecAction "nolog,phase:1,initcol:RESOURCE=%{REQUEST_FILENAME}"

SecArgumentsLimit #

Description: Configures the maximum number of ARGS that will be accepted for processing.

Syntax: SecArgumentsLimit [LIMIT]

Default: 1000

Exceeding the limit will not be included. With JSON body processing, there is nothing to do when exceed the limit. Example:

SecArgumentsLimit 1000

SecAuditEngine #

Description: Configures the audit logging engine.

Syntax: SecAuditEngine RelevantOnly

Default: Off

The SecAuditEngine directive is used to configure the audit engine, which logs complete transactions.

The possible values for the audit log engine are as follows:

• On: log all transactions
• Off: do not log any transactions
• RelevantOnly: only the log transactions that have triggered a warning or an error, or have a status code that is considered to be relevant (as determined by the SecAuditLogRelevantStatus directive)

Note: If you need to change the audit log engine configuration on a per-transaction basis (e.g., in response to some transaction data), use the ctl action.

The following example demonstrates how SecAuditEngine is used:

SecAuditEngine RelevantOnly
SecAuditLog logs/audit/audit.log
SecAuditLogParts ABCFHZ
SecAuditLogType concurrent
SecAuditLogStorageDir logs/audit
SecAuditLogRelevantStatus ^(?:5|4(?!04))

SecAuditLog #

Description: Defines the path to the main audit log file (serial logging format) or the concurrent logging index file (concurrent logging format).

Syntax: SecAuditLog [ABSOLUTE_PATH_TO_LOG_FILE]

When used in combination with mlogc (only possible with concurrent logging), this directive defines the mlogc location and command line.

Example:

SecAuditLog "/path/to/audit.log"

Note: This audit log file is opened on startup when the server typically still runs as root. You should not allow non-root users to have write privileges for this file or for the directory.

SecAuditLogDirMode #

Description: Configures the mode (permissions) of any directories created for the concurrent audit logs, using an octal mode value as parameter (as used in chmod).

Syntax: SecAuditLogDirMode octal_mode|"default"

Default: 0600

The default mode for new audit log directories (0600) only grants read/write access to the owner.

Example:

SecAuditLogDirMode 02750

SecAuditLogFileMode #

Description: Configures the mode (permissions) of any files created for concurrent audit logs using an octal mode (as used in chmod). See SecAuditLogDirMode for controlling the mode of created audit log directories.

Syntax: SecAuditLogFileMode octal_mode|"default"

Default: 0600

Example:

SecAuditLogFileMode 00640

SecAuditLogFormat #

Description: Select the output format of the AuditLogs. The format can be either the native AuditLogs format or JSON.

Syntax: SecAuditLogFormat JSON|Native

Default: Native

SecAuditLogParts #

Description: Defines which parts of each transaction are going to be recorded in the audit log. Each part is assigned a single letter; when a letter appears in the list then the equivalent part will be recorded. See below for the list of all parts.

Syntax: SecAuditLogParts [PARTLETTERS]

Default: ABCFHZ

The format of the audit log format is documented in detail in the Audit Log Data Format Documentation.

Example:

SecAuditLogParts ABCFHZ

Available audit log parts:

• A: Audit log header (mandatory).
• B: Request headers.
• C: Request body (present only if the request body exists and Coraza is configured to intercept it. This would require SecRequestBodyAccess to be set to on).
• D: Reserved for intermediary response headers; not implemented yet.
• E: Intermediary response body (present only if Coraza is configured to intercept response bodies, and if the audit log engine is configured to record it. Intercepting response bodies requires SecResponseBodyAccess to be enabled). Intermediary response body is the same as the actual response body unless Coraza intercepts the intermediary response body, in which case the actual response body will contain the error message.
• F: Final response headers.
• G: Reserved for the actual response body; not implemented yet.
• H: Audit log trailer.
• I: This part is a replacement for part C. It will log the same data as C in all cases except when multipart/form-data encoding in used. In this case, it will log a fake application/x-www-form-urlencoded body that contains the information about parameters but not about the files. This is handy if you don’t want to have (often large) files stored in your audit logs.
• J: This part contains information about the files uploaded using multipart/form-data encoding.
• K: This part contains a full list of every rule that matched (one per line) in the order they were matched. The rules are fully qualified and will thus show inherited actions and default operators.
• Z: Final boundary, signifies the end of the entry (mandatory).

SecAuditLogRelevantStatus #

Description: Configures which response status code is to be considered relevant for the purpose of audit logging.

Syntax: SecAuditLogRelevantStatus [REGEX]

The main purpose of this directive is to allow you to configure audit logging for only the transactions that have the status code that matches the supplied regular expression.

Example:

SecAuditLogRelevantStatus "^(?:5|40[1235])"

This example would log all 5xx and 4xx level status codes, except for 404s. Although you could achieve the same effect with a rule in phase 5, SecAuditLogRelevantStatus is sometimes better, because it continues to work even when SecRuleEngine is disabled.

Note: Must have SecAuditEngine set to RelevantOnly. Additionally, the auditlog action is present by default in rules, this will make the engine bypass the SecAuditLogRelevantStatus and send rule matches to the audit log regardless of status. You must specify noauditlog in the rules manually or set it in SecDefaultAction.

SecDebugLog #

Description: Path to the Coraza debug log file.

Syntax: SecDebugLog [ABSOLUTE_PATH_TO_DEBUG_LOG]

Logs will be written to this file. Make sure the process user has write access to the directory.

SecDebugLogLevel #

Description: Configures the verboseness of the debug log data.

Syntax: SecDebugLogLevel [LOG_LEVEL]

Default: 3

Depending on the implementation, errors ranging from 1 to 2 might be directly logged to the connector error log. For example, level 1 (error) logs will be written to caddy server error logs. The possible values for the debug log level are:

• 0: No logging (least verbose)
• 1: Error
• 2: Warn
• 3: Info
• 4-8: Debug
• 9: Trace (most verbose)

Levels outside the 0-9 range will default to level 3 (Info)

SecDefaultAction #

Description: Defines the default list of actions, which will be inherited by the rules in the same configuration context.

Syntax: SecDefaultAction "phase:2,log,auditlog,deny,status:403,tag:'SLA 24/7'"

Default: phase:2,log,auditlog,pass

Every rule following a previous SecDefaultAction directive in the same configuration context will inherit its settings unless more specific actions are used.

Rulesets like OWASP Core Ruleset uses this to define operation modes:

• You can set the default disruptive action to block for phases 1 and 2 and you can force a phase 3 rule to be disrupted if the thread score is high.
• You can set the default disruptive action to deny and each risky rule will interrupt the connection.

Important: Every SecDefaultAction directive must specify a disruptive action and a processing phase and cannot contain metadata actions.

SecMarker #

Description: Adds a fixed rule marker that can be used as a target in a skipAfter action. A SecMarker directive essentially creates a rule that does nothing and whose only purpose is to carry the given ID.

Syntax: SecMarker [ID|TEXT]

The value can be either a number or a text string. The SecMarker directive is available to allow you to choose the best way to implement a skip-over. Here is an example used from the Core Rule Set:

	SecMarker BEGIN_HOST_CHECK

	SecRule &REQUEST_HEADERS:Host "@eq 0" \
		"id:'960008',skipAfter:END_HOST_CHECK,phase:2,rev:'2.1.1',\
		t:none,block,msg:'Request Missing a Host Header',\
		tag:'PROTOCOL_VIOLATION/MISSING_HEADER_HOST',tag:'WASCTC/WASC-21',\
		tag:'OWASP_TOP_10/A7',tag:'PCI/6.5.10',\
		severity:'5',setvar:'tx.msg=%{rule.msg}',setvar:tx.anomaly_score=+%{tx.notice_anomaly_score},\
		setvar:tx.protocol_violation_score=+%{tx.notice_anomaly_score},\
		setvar:tx.%{rule.id}-PROTOCOL_VIOLATION/MISSING_HEADER-%{matched_var_name}=%{matched_var}"
	SecRule REQUEST_HEADERS:Host "^$" \
		"id:'960008',phase:2,rev:'2.1.1',t:none,block,msg:'Request Missing a Host Header',\
		tag:'PROTOCOL_VIOLATION/MISSING_HEADER_HOST',tag:'WASCTC/WASC-21',\
		tag:'OWASP_TOP_10/A7',tag:'PCI/6.5.10',severity:'5',\
		setvar:'tx.msg=%{rule.msg}',setvar:tx.anomaly_score=+%{tx.notice_anomaly_score},\
		setvar:tx.protocol_violation_score=+%{tx.notice_anomaly_score},\
		setvar:tx.%{rule.id}-PROTOCOL_VIOLATION/MISSING_HEADER-%{matched_var_name}=%{matched_var}"

	SecMarker END_HOST_CHECK

SecRequestBodyAccess #

Description: Configures whether request bodies will be buffered and processed by Coraza.

Syntax: SecRequestBodyAccess On|Off

Default: Off

This directive is required if you want to inspect the data transported request bodies (e.g., POST parameters). Request buffering is also required in order to make reliable blocking possible. The possible values are:

• On: buffer request bodies
• Off: do not buffer request bodies

SecRequestBodyInMemoryLimit #

Description: Configures the maximum request body size that Coraza will store in memory.

Syntax: SecRequestBodyInMemoryLimit [LIMIT_IN_BYTES]

Default: 131072 (128 KB)

When a multipart/form-data request is being processed, once the in-memory limit is reached, the request body will start to be streamed into a temporary file on disk.

SecRequestBodyLimit #

Description: Configures the maximum request body size Coraza will accept for buffering.

Syntax: SecRequestBodyLimit [LIMIT_IN_BYTES]

Default: 134217728 (131072 KB)

Anything over the limit will be rejected with status code 413 (Request Entity Too Large). There is a hard limit of 1 GB.

SecRequestBodyLimitAction #

Description: Controls what happens once a request body limit, configured with SecRequestBodyLimit, is encountered

Syntax: SecRequestBodyLimitAction Reject|ProcessPartial

Default: Reject

By default, Coraza will reject a request body that is longer than specified to avoid OOM issues while buffering the request body prior the inspection.

SecRequestBodyNoFilesLimit #

Description: Configures the maximum request body size Coraza will accept for buffering, excluding the size of any files being transported in the request. This directive is useful to reduce susceptibility to DoS attacks when someone is sending request bodies of very large sizes. Web applications that require file uploads must configure SecRequestBodyLimit to a high value, but because large files are streamed to disk, file uploads will not increase memory consumption. However, it’s still possible for someone to take advantage of a large request body limit and send non-upload requests with large body sizes. This directive eliminates that loophole.

Syntax: SecRequestBodyNoFilesLimit 131072

Default: 1048576 (1 MB)

Generally speaking, the default value is not small enough. For most applications, you should be able to reduce it down to 128 KB or lower. Anything over the limit will be rejected with status code 413 (Request Entity Too Large). There is a hard limit of 1 GB.

SecResponseBodyAccess #

Description: Configures whether response bodies are to be buffered.

Syntax: SecResponseBodyAccess On|Off

Default: Off

This directive is required if you plan to inspect HTML responses and implement response blocking. Possible values are:

• On: buffer response bodies (but only if the response MIME type matches the list configured with SecResponseBodyMimeType).
• Off: do not buffer response bodies.

SecResponseBodyLimit #

Description: Configures the maximum response body size that will be accepted for buffering.

Syntax: SecResponseBodyLimit [LIMIT_IN_BYTES]

Default: 524288 (512 KB)

Anything over this limit will be rejected with status code 500 (Internal Server Error). This setting will not affect the responses with MIME types that are not selected for buffering. There is a hard limit of 1 GB.

SecResponseBodyLimitAction #

Description: Controls what happens once a response body limit, configured with SecResponseBodyLimit, is encountered.

Syntax: SecResponseBodyLimitAction Reject|ProcessPartial

By default, Coraza will reject a response body that is longer than specified. Some web sites, however, will produce very long responses, making it difficult to come up with a reasonable limit. Such sites would have to raise the limit significantly to function properly, defying the purpose of having the limit in the first place (to control memory consumption). With the ability to choose what happens once a limit is reached, site administrators can choose to inspect only the first part of the response, the part that can fit into the desired limit, and let the rest through. Some could argue that allowing parts of responses to go uninspected is a weakness. This is true in theory, but applies only to cases in which the attacker controls the output (e.g., can make it arbitrary long). In such cases, however, it is not possible to prevent leakage anyway. The attacker could compress, obfuscate, or even encrypt data before it is sent back, and therefore bypass any monitoring device.

SecRule #

Description: Creates a rule that will analyze the selected variables using the selected operator.

Syntax: SecRule VARIABLES OPERATOR [ACTIONS]

Every rule must provide one or more variables along with the operator that should be used to inspect them. If no actions are provided, the default list will be used. (There is always a default list, even if one was not explicitly set with SecDefaultAction.) If there are actions specified in a rule, they will be merged with the default list to form the final actions that will be used. (The actions in the rule will overwrite those in the default list.) Refer to SecDefaultAction for more information.

Example:

SecRule ARGS "@rx attack" "phase:1,log,deny,id:1"

SecRuleEngine #

Description: Configures the rules engine.

Syntax: SecRuleEngine On|Off|DetectionOnly

Default: Off

The possible values are:

• On: process rules
• Off: do not process rules
• DetectionOnly: process rules but never executes any disruptive actions (block, deny, drop, allow, proxy and redirect)

SecRuleRemoveByID #

Description: Removes the matching rules from the current configuration context.

Syntax: SecRuleRemoveById ...[ID OR RANGE]

SecRuleRemoveByTag #

Description: Removes the matching rules from the current configuration context.

Syntax: SecRuleRemoveByTag [TAG]

Normally, you would use SecRuleRemoveById to remove rules, but it may occasionally be easier to disable an entire group of rules with SecRuleRemoveByTag. Matching is by case-sensitive string equality.

Example:

SecRuleRemoveByTag attack-dos

Note: OWASP CRS has a list of supported tags https://coreruleset.org/docs/rules/metadata/