Logstash filter string anywhere

Elastic Stack Logstash
1

Hi there,

I want to filter firewall logs if some specific string matches anywhere in the message and do not know exactly how to do it.

Sample Log message:
{"zone_src":"SOURCE","zone_dst":"EXTERNAL","reason":"rule","rule_id":123456,"rule_description":"Description","action":"ACCEPT","@timestamp":"2022-09-XXT0X:52:12.123123+0200","timestamp":12345678,"timestamp_usec":123123,"iface_in":"eth11.1111","iface_out":"eth2.111","ip_src":"1.1.1.1","ip_dst":"2.2.2.2","protocol":6,"port_src":54321,"port_dst":2345,"mark":17825392,"tos":1,"host_id":164119,"host_name":"hostname","logtype":"forward"}

I want to get all Logs containing "zone_dst":"EXTERNAL"

I tried it with:

filter {
        grok {
           match => { "message" => "("zone_dst":"External")"
                 }
        }

but that doesn't work.

Does anyone of you can assist me?

Thank you very much!

Max

2

If your logs are always in JSON format you may have better luck using the JSON filter plugin: JSON filter plugin | Logstash Reference [8.4] | Elastic

Example:

filter {
  json {
    source => "message"
  }
}

You can then use a conditional to do something if the value is External EG:

if [zone_dst] == "External" {
  #do something
}

Alternatively, if you only want to ship events with the value of 'External' you could invert the above conditional and use the Drop filter plugin (Drop filter plugin | Logstash Reference [8.4] | Elastic):

if [zone_dst] != "External" {
  drop { }
}
3

Hi Steve,

I tried it like this, but I got an configuration error:

input {
        tcp {
                port => 10516
                type => syslog
        }
}
filter {
        json {
           source =>  "message"
                if [zone_dst] != "External" {
                drop {}
                }
        }
kv {
           source => "message"
           field_split => ","
           value_split => ":"
           trim_key => "{\\\""
           trim_value => "\\\"}"
           #target_field => "details"
           include_brackets => false
    }
}

The error is:

[2022-09-16T11:30:04,199][ERROR][logstash.agent ] Failed to execute action {:action=>LogStash::PipelineAction::Create/pipeline_id:main, :exception=>"LogStash::ConfigurationError", :message=>"Expected one of [ \t\r\n], "#", "=>" at line 10, column 6 (byte 101) after filter {\n\tjson {\n\t source => "message"\n\t\tif ",

4

You cannot have an IF conditiona inside the json filter.

You also do not need the kv filter, the json filter will parse your message.

You just need this:

input {
        tcp {
                port => 10516
                type => syslog
        }
}
filter {
        json {
           source =>  "message"
        }
        if [zone_dst] != "EXTERNAL" {
            drop {}
        }
}

In your log you have EXTERNAL, not External, so you need to match the exact value.

5

Hi Leandro,

thank you for your hints.
Now logstash starts correctly, but it seems that it doesn't recognize the message as json:

[2022-09-16T22:17:02,018][WARN ][logstash.filters.json    ][main][9bee16fd531aafb8069711ca7a54cf6070ab1d5419a8d3b5ca4b7cd7cb23f174] Error parsing json {:source=>"message", :raw=>"528 <13>1 2022-09-16T22:17:01+02:00 1.1.1.1 REPLACED - - - {\"zone_src\":\"REPLACED\",\"zone_dst\":\"EXTERNAL\",\"reason\":\"rule\",\"rule_id\":12345,\"rule_description\":\"REPLACED\",\"action\":\"ACCEPT\",\"@timestamp\":\"2022-09-16T22:17:00.912286+0200\",\"timestamp\":1663359420,\"timestamp_usec\":912286,\"iface_in\":\"eth12.345\",\"iface_out\":\"eth67.890\",\"ip_src\":\"2.2.2.2\",\"ip_dst\":\"3.3.3.3\",\"protocol\":17,\"port_src\":12345,\"port_dst\":12345,\"mark\":17825792,\"tos\":0,\"host_id\":164119,\"host_name\":\"REPLACED\",\"logtype\":\"forward\"}", :exception=>#<LogStash::Json::ParserError: Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')```

It seems that syslog-ng adds the "<13>" before sending it to logstash.

Here is my syslog-ng conf regarding logstash:

source s_network_test {
  network(
    ip("0.0.0.0")
    log_iw_size(10000)
    log_fetch_limit(1000)
    transport("udp")
    port(514)
    flags(dont-store-legacy-msghdr,no-parse));
};

rewrite r_test { set("test", value("PROGRAM")); };

destination d_logstash_test {
  syslog("X.X.X.X" transport("tcp") port(12345)
        template("$(format-json --scope dot-nv-pairs)")
  );
 };

log {
source(s_network_test);
rewrite(r_test);
destination(d_logstash_test);
flags(flow-control);
};

Thank you so much!

BR,
Max

6

Can you post a full and complete log line redacting any sensitive information? You may want to look at Syslog input plugin | Logstash Reference [8.4] | Elastic if you are sending syslogs, you can then parse the syslog and then run the JSON filter against the syslog message rather than the full line

7

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