https://github.com/fox-it/pcap-broker
PCAP-over-IP server written in Golang
https://github.com/fox-it/pcap-broker
attack-defense-ctf ctf ctf-tool network-analysis pcap pcap-over-ip peecap tcpdump
Last synced: 9 months ago
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PCAP-over-IP server written in Golang
- Host: GitHub
- URL: https://github.com/fox-it/pcap-broker
- Owner: fox-it
- License: apache-2.0
- Created: 2023-07-11T14:50:28.000Z (almost 3 years ago)
- Default Branch: main
- Last Pushed: 2025-06-02T18:54:14.000Z (about 1 year ago)
- Last Synced: 2025-07-02T12:48:17.862Z (12 months ago)
- Topics: attack-defense-ctf, ctf, ctf-tool, network-analysis, pcap, pcap-over-ip, peecap, tcpdump
- Language: Go
- Homepage:
- Size: 25.4 KB
- Stars: 21
- Watchers: 7
- Forks: 3
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# pcap-broker
`pcap-broker` is a tool to capture network traffic and make this available to one or more clients via PCAP-over-IP.
PCAP-over-IP can be useful in situations where low latency is a priority, for example during Attack and Defend CTFs.
More information on PCAP-over-IP can be found here:
* https://www.netresec.com/?page=Blog&month=2022-08&post=What-is-PCAP-over-IP
`pcap-broker` supports the following features:
* Distributing packet data to one or more PCAP-over-IP clients
* Execute a command to capture traffic, usually `tcpdump` (expects stdout to be pcap data)
* `pcap-broker` will exit if the capture command exits
## Building
Building `pcap-broker` requires the `libpcap` development headers, on Debian you can install it with:
```shell
$ apt install libpcap-dev
```
To build from source, clone this repository and run:
```shell
$ go build .
$ ./pcap-broker --help
```
Or you can build the Docker container:
```shell
$ docker build -t pcap-broker .
$ docker run -it pcap-broker --help
```
Alternatively, install directly using `go`:
```shell
$ go install github.com/fox-it/pcap-broker@latest
$ pcap-broker --help
```
## Running
```shell
$ ./pcap-broker --help
Usage of ./pcap-broker:
-cmd string
command to execute for pcap data (eg: tcpdump -i eth0 -n --immediate-mode -s 65535 -U -w -)
-debug
enable debug logging
-json
enable json logging
-listen string
listen address for pcap-over-ip (eg: localhost:4242)
-n disable reverse lookup of connecting PCAP-over-IP client IP address
```
Arguments can be passed via commandline:
```shell
$ ./pcap-broker -cmd "sudo tcpdump -i eth0 -n --immediate-mode -s 65535 -U -w -"
```
Or alternatively via environment variables:
```shell
LISTEN_ADDRESS=:4242 PCAP_COMMAND='sudo tcpdump -i eth0 -n --immediate-mode -s 65535 -U -w -' ./pcap-broker
```
Using environment variables is useful when you are using `pcap-broker` in a Docker setup.
Now you can connect to it via TCP and stream PCAP data using `nc` and `tcpdump`:
```shell
$ nc -v localhost 4242 | tcpdump -nr -
```
Or use a tool that natively supports PCAP-over-IP, for example `tshark`:
```shell
$ tshark -i TCP@localhost:4242
```
# Acquiring PCAP data over SSH
One use case is to acquire PCAP from a remote machine over SSH and make this available via PCAP-over-IP.
Such a use case, including an example SSH command to bootstrap this, has been documented in the `docker-compose.yml.example` file:
```yaml
services:
pcap-broker-remote-host:
image: pcap-broker:latest
container_name: pcap-broker-remote-host
restart: always
volumes:
# Mount the private key into container that wil be used for SSH
# Ensure that on the `remote-host` the public key is in the /root/.ssh/authorized_keys file.
- ~/.ssh/id_ed25519:/root/.ssh/id_ed25519:ro
environment:
# Command that will be executed by pcap-broker to read PCAP data.
# Which is to SSH into `remote-host` and run tcpdump on eth0 and write PCAP data to stdout.
# The `not port 22` BPF is necessary to avoid any traffic loops as the PCAP data is transferred over SSH.
PCAP_COMMAND: |-
ssh root@remote-host -oStrictHostKeyChecking=no
tcpdump -U --immediate-mode -ni eth0 -s 65535 -w - not port 22
# Bind on 0.0.0.0 port 4242. From within the same Docker network you can reach it using the `container_name`
# For example in another Docker service you can reach this pcap-broker using `pcap-broker-remote-host:4242`
LISTEN_ADDRESS: "0.0.0.0:4242"
ports:
# This is optional, but makes the PCAP-over-IP port also available locally on the Docker host on port 4200.
# Handy for debugging, for example: `nc -v localhost 4200 | tcpdump -nr -`
- 127.0.0.1:4200:4242
```
## Background
This tool was initially written for Attack & Defend CTF purposes but can be useful in other situations where low latency is preferred, or whenever a no-nonsense PCAP-over-IP server is needed. During the CTF that Fox-IT participated in, `pcap-broker` allowed the Blue Team to capture network data once and disseminate this to other tools that natively support PCAP-over-IP, such as:
* [Arkime](https://arkime.com/) ([docs](https://arkime.com/settings#reader-poi))
* [Tulip](https://github.com/OpenAttackDefenseTools/tulip) ([#24](https://github.com/OpenAttackDefenseTools/tulip/pull/24))
* [Shovel](https://github.com/FCSC-FR/shovel)
* [Pkappa2](https://github.com/spq/pkappa2)
* WireShark's [dumpcap](https://www.wireshark.org/docs/man-pages/dumpcap.html) and [tshark](https://www.wireshark.org/docs/man-pages/tshark.html) (`-i TCP@:`)
* Zeek's [zeek-pcapovertcp-plugin](https://github.com/emnahum/zeek-pcapovertcp-plugin)