6.29. MQTT Keywords

Various keywords can be used for matching on fields in fixed and variable headers of MQTT messages as well as payload values.

6.29.1. mqtt.protocol_version

Match on the value of the MQTT protocol version field in the fixed header.

The format of the keyword:

mqtt.protocol_version:<min>-<max>;
mqtt.protocol_version:[<|>]<number>;
mqtt.protocol_version:<value>;

Examples:

mqtt.protocol_version:5;

6.29.2. mqtt.type

Match on the MQTT message type (also: control packet type). Valid values are :

  • CONNECT
  • CONNACK
  • PUBLISH
  • PUBACK
  • PUBREC
  • PUBREL
  • PUBCOMP
  • SUBSCRIBE
  • SUBACK
  • UNSUBSCRIBE
  • UNSUBACK
  • PINGREQ
  • PINGRESP
  • DISCONNECT
  • AUTH
  • UNASSIGNED

where UNASSIGNED refers to message type code 0.

Examples:

mqtt.type:CONNECT;
mqtt.type:PUBLISH;

6.29.3. mqtt.flags

Match on a combination of MQTT header flags, separated by commas (,). Flags may be prefixed by ! to indicate negation, i.e. a flag prefixed by ! must not be set to match.

Valid flags are:

  • dup (duplicate message)
  • retain (message should be retained on the broker)

Examples:

mqtt.flags:dup,!retain;
mqtt.flags:retain;

6.29.4. mqtt.qos

Match on the Quality of Service request code in the MQTT fixed header. Valid values are:

  • 0 (fire and forget)
  • 1 (at least one delivery)
  • 2 (exactly one delivery)

Examples:

mqtt.qos:0;
mqtt.qos:2;

6.29.5. mqtt.reason_code

Match on the numeric value of the reason code that is used in MQTT 5.0 for some message types. Please refer to the specification for the meaning of these values, which are often specific to the message type in question.

Examples:

# match on attempts to unsubscribe from a non-subscribed topic
mqtt.type:UNSUBACK; mqtt.reason_code:17;

# match on publications that were accepted but there were no subscribers
mqtt.type:PUBACK; mqtt.reason_code:16;

# match on connection attempts by banned clients
mqtt.CONNACK; mqtt.reason_code:138;

# match on failed connection attempts due to bad credentials
mqtt.CONNACK; mqtt.reason_code:134;

# match on connections terminated by server shutdowns
mqtt.DISCONNECT; mqtt.reason_code:139;

This keyword is also available under the alias mqtt.connack.return_code for completeness.

6.29.6. mqtt.connack.session_present

Match on the MQTT CONNACK session_present flag. Values can be yes, true, no or false.

Examples:

mqtt.CONNACK; mqtt.connack.session_present:true;

6.29.7. mqtt.connect.clientid

Match on the self-assigned client ID in the MQTT CONNECT message.

Examples:

mqtt.connect.clientid; pcre:"/^mosq.*/";
mqtt.connect.clientid; content:"myclient";

mqtt.connect.clientid is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.8. mqtt.connect.flags

Match on a combination of MQTT CONNECT flags, separated by commas (,). Flags may be prefixed by ! to indicate negation, i.e. a flag prefixed by ! must not be set to match.

Valid flags are:

  • username (message contains a username)
  • password (message contains a password)
  • will (message contains a will definition)
  • will_retain (will should be retained on broker)
  • clean_session (start with a clean session)

Examples:

mqtt.connect.flags:username,password,!will;
mqtt.connect.flags:username,!password;
mqtt.connect.flags:clean_session;

6.29.9. mqtt.connect.password

Match on the password credential in the MQTT CONNECT message.

Examples:

mqtt.connect.password; pcre:"/^123[0-9]*/";
mqtt.connect.password; content:"swordfish";

mqtt.connect.password is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.10. mqtt.connect.username

Match on the username credential in the MQTT CONNECT message.

Examples:

mqtt.connect.username; content:"benson";

mqtt.connect.username is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.11. mqtt.connect.willmessage

Match on the will message in the MQTT CONNECT message, if a will is defined.

Examples:

mqtt.connect.willmessage; pcre:"/^fooba[rz]/";
mqtt.connect.willmessage; content:"hunter2";

mqtt.connect.willmessage is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.12. mqtt.connect.willtopic

Match on the will topic in the MQTT CONNECT message, if a will is defined.

Examples:

mqtt.connect.willtopic; pcre:"/^hunter[0-9]/";

mqtt.connect.willtopic is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.13. mqtt.publish.message

Match on the payload to be published in the MQTT PUBLISH message.

Examples:

mqtt.type:PUBLISH; mqtt.publish.message; pcre:"/uid=[0-9]+/";
# match on published JPEG images
mqtt.type:PUBLISH; mqtt.publish.message; content:"|FF D8 FF E0|"; startswith;

mqtt.publish.message is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.14. mqtt.publish.topic

Match on the topic to be published to in the MQTT PUBLISH message.

Examples:

mqtt.publish.topic; content:"mytopic";

mqtt.publish.topic is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.15. mqtt.subscribe.topic

Match on any of the topics subscribed to in a MQTT SUBSCRIBE message.

Examples:

mqtt.subscribe.topic; content:"mytopic";

mqtt.subscribe.topic is a ‘sticky buffer’ and can be used as fast_pattern.

6.29.16. mqtt.unsubscribe.topic

Match on any of the topics unsubscribed from in a MQTT UNSUBSCRIBE message.

Examples:

mqtt.unsubscribe.topic; content:"mytopic";

mqtt.unsubscribe.topic is a ‘sticky buffer’ and can be used as fast_pattern.