Collecting port scans -- "Ignore empty non-FIN packet"

(Stephen Cope) #1

How can I collect the opening packet in a port scan (ie, the SYN before the handshake is completed) using Packetbeat?

I'm using pcap with bpf_filter to select all TCP/IP traffic from a variety of ports. Unfortunately this does not capture port scans. The explanation (when I ran packetbeat -d "*" ) is that the non-FIN (ie, SYN packet) is discarded:

decoder.go:179: DBG Ignore empty non-FIN packet

When I dump to a file using the -dump argument I do see the packets listed there, however, they are not submitted to ElasticSearch because they are discarded.

This is the configuration that I'm using:

device: any
type: pcap
snaplen: 1514
buffer_size_mb: 10
bpf_filter: "port 23 or port 2323 or port 6789"

(Stephen Cope) #2

Example command line:

sudo packetbeat -c packetbeat_raw.yml -d "*" -dump /tmp/tcp-out

Output from tcpdump:

tcpdump -r /tmp/tcp-out -n
10:25:17.978102 IP > x.x.x.x.telnet: Flags [S], seq 758585095, win 60867, length 0
10:25:17.995765 IP x.x.x.x.telnet > Flags [R.], seq 0, ack 758585096, win 0, length 0

(system) #3

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