[Snort-devel] Odd bug when using alert_json plugin

Noah Dietrich noah_dietrich at 86penny.org
Wed Jun 13 03:20:32 EDT 2018

I'm playing around with the alert_json plugin, and i found a bit of odd

When running snort in alert mode, it correctly created the
/var/log/snort/alert_json.txt file and filled it with events (about 17 MB
of data in that file). I then restarted snort and pushed a huge amount of
data at it (sudo ping -c 10000 -i .001 -s 4046, and snort
created a new file with the timestamp (alert_json.txt.1528868120), even
though the first file hadn't filled up and filled it with 100 MB of data.

I then re-ran snort, with a smaller dataset from local pcaps, and it
appended the events to the original alert_json.txt file.

I'd call this an odd bug because most applications that consume the json
files will ignore the first file once the second file is created. I'd say
there are two issues here:
1. Snort rolled over to the second json file early, before the original one
(without the timestamp) was full. I'm not sure if this was because of the
large ammount of data i threw at it with the ping command above.
2. snort appended alert data to the original alert_json file because it
wasn't full, even though there was a newer (by UTC timestamp) json file in
the directory.

i'd recommend that snort not create an initial alert_json file without a
timestamp if no alert_json files exist, just so there are no differences
between the output files.

I am running snort with community rules installed (unmodified), two of my
own local rules (one that alerts on icmp traffic), and builtin rules

First run:
sudo snort -c /usr/local/etc/snort/snort.lua --pcap-filter \*.pcap
--pcap-dir ~/snort_src/Pcaps -R
/usr/local/etc/snort/rules/snort3-community.rules -A alert_json -s 65535 -k
none -l /var/log/snort

Second run:
sudo snort -c /usr/local/etc/snort/snort.lua -i ens160 -l /var/log/snort -A
alert_json  -R /usr/local/etc/snort/rules/snort3-community.rules --warn-all

third run:
sudo snort -c /usr/local/etc/snort/snort.lua -r ~/maccdc2012_00000.pcap -R
/usr/local/etc/snort/rules/snort3-community.rules -A alert_json -s 65535 -k
none -l /var/log/snort
(note: pcap from
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