Global-Thresholds ================= Thresholds can be configured in the rules themselves, see :doc:`../rules/thresholding`. They are often set by rule writers based on their intel for creating a rule combined with a judgement on how often a rule will alert. Next to these settings, thresholding can be configured on the sensor using the threshold.config. threshold/event_filter ~~~~~~~~~~~~~~~~~~~~~~ Syntax: :: threshold gen_id , sig_id , type , track , count , seconds rate_filter ~~~~~~~~~~~ TODO suppress ~~~~~~~~ Suppressions can be used to suppress alerts for a rule or a host/network. Actions performed when a rule matches, such as setting a flowbit, are still performed. Syntax: :: suppress gen_id , sig_id suppress gen_id , sig_id , track , ip Examples: :: suppress gen_id 1, sig_id 2002087, track by_src, ip 209.132.180.67 This will make sure the signature 2002087 will never match for src host 209.132.180.67. Other possibilities/examples:: suppress gen_id 1, sig_id 2003614, track by_src, ip 217.110.97.128/25 suppress gen_id 1, sig_id 2003614, track by_src, ip [192.168.0.0/16,10.0.0.0/8,172.16.0.0/12] suppress gen_id 1, sig_id 2003614, track by_src, ip $HOME_NET .. _global-thresholds-vs-rule-thresholds: Global thresholds vs rule thresholds ------------------------------------ **Note: this section applies to 1.4+ In 1.3 and before mixing rule and global thresholds is not supported.** When a rule has a threshold/detection_filter set a rule can still be affected by the global threshold file. The rule below will only fire if 10 or more emails are being delivered/sent from a host within 60 seconds. :: alert tcp any any -> any 25 (msg:"ET POLICY Inbound Frequent Emails - Possible Spambot Inbound"; \ flow:established; content:"mail from|3a|"; nocase; \ threshold: type threshold, track by_src, count 10, seconds 60; \ reference:url,doc.emergingthreats.net/2002087; classtype:misc-activity; sid:2002087; rev:10;) Next, we'll see how global settings affect this rule. Suppress ~~~~~~~~ Suppressions can be combined with rules with thresholds/detection_filters with no exceptions. :: suppress gen_id 1, sig_id 2002087, track by_src, ip 209.132.180.67 suppress gen_id 0, sig_id 0, track by_src, ip 209.132.180.67 suppress gen_id 1, sig_id 0, track by_src, ip 209.132.180.67 Each of the rules above will make sure 2002087 doesn't alert when the source of the emails is 209.132.180.67. It **will** alert for all other hosts. :: suppress gen_id 1, sig_id 2002087 This suppression will simply convert the rule to "noalert", meaning it will never alert in any case. If the rule sets a flowbit, that will still happen. Threshold/event_filter ~~~~~~~~~~~~~~~~~~~~~~ When applied to a specific signature, thresholds and event_filters (threshold from now on) will override the signature setting. This can be useful for when the default in a signature doesn't suit your evironment. :: threshold gen_id 1, sig_id 2002087, type both, track by_src, count 3, seconds 5 threshold gen_id 1, sig_id 2002087, type threshold, track by_src, count 10, seconds 60 threshold gen_id 1, sig_id 2002087, type limit, track by_src, count 1, seconds 15 Each of these will replace the threshold setting for 2002087 by the new threshold setting. **Note:** overriding all gids or sids (by using gen_id 0 or sig_id 0) is not supported. Bug #425. Rate_filter ~~~~~~~~~~~ TODO