Snort で syslog (具体的には auth.log) へのロギングを停止できないようです。私が知る限り、-s引数または構成で実行しているかのように動作しているようですoutput alert_syslog: LOG_AUTH LOG_ALERT。
でコンパイルされた snort 2.9.7.0 を実行して./configure --enable-reloadいますが、不足している隠しオプションがない限り、merged.log に unified2 としてログを記録し、それ以外の場所にはログを記録しないように指示しています。
snort@snort:~$ ps -ef | grep snort
snort 7524 1 1 18:15 ? 00:00:00 /usr/bin/snort -c /etc/snort/snort.conf -i bond0.566 -l /var/log/snort/bond0.566 -D
snort@snort:~$ grep -R '^output' /etc/snort
/etc/snort/snort.conf:output unified2: filename merged.log, limit 128, mpls_event_types, vlan_event_types
ここに私が見ているログのいくつかがあります
snort@snort:~$ tail -n 10 /var/log/auth.log
Feb 10 18:31:15 snort.example.com snort[32353]: [119:31:1] http_inspect: UNKNOWN METHOD [Classification: Unknown Traffic] [Priority: 3]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:32271 -> xxx.xxx.xxx.xxx:80
Feb 10 18:31:15 snort.example.com snort[32353]: [119:31:1] http_inspect: UNKNOWN METHOD [Classification: Unknown Traffic] [Priority: 3]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:32271 -> xxx.xxx.xxx.xxx:80
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:56534 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:56534 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:53271 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:53271 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:5:1] stream5: Bad segment, overlap adjusted size less than/equal 0 [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:53271 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:5:1] stream5: Bad segment, overlap adjusted size less than/equal 0 [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:53271 -> xxx.xxx.xxx.xxx:443
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:2443 -> xxx.xxx.xxx.xxx:80
Feb 10 18:31:15 snort.example.com snort[32353]: [129:12:1] stream5: TCP Small Segment Threshold Exceeded [Classification: Potentially Bad Traffic] [Priority: 2]: <bond0.566> {TCP} xxx.xxx.xxx.xxx:2443 -> xxx.xxx.xxx.xxx:80
これらのアラートのほとんどはゴミであり、後で除外します。アラート自体は気にしません。気になるのは、アラートが auth.log に送られ、その理由がわかりません。