[![Build masscanned](https://github.com/ivre/masscanned/actions/workflows/test.yml/badge.svg?branch=master)](https://github.com/ivre/masscanned/actions/workflows/test.yml?branch=master)

# Masscanned

**Masscanned** (name inspired, of course, by [masscan](https://github.com/robertdavidgraham/masscan))
is a network responder. Its purpose is to provide generic answers to as many protocols as possible,
and with as few assumptions as possible on the client's intentions.

> *Let them talk first.*

Just like [masscan](https://github.com/robertdavidgraham/masscan), **masscanned** implements its own,
userland network stack, similarly to [honeyd](http://honeyd.org/). It is designed to interact
with scanners and opportunistic bots as far as possible, and to support as many protocols as possible.

For example, when it receives network packets:

* **masscanned** answers to `ARP who is-at` with `ARP is-at` (for its IP addresses),
* **masscanned** answers to `ICMP Echo Request` with `ICMP Echo Reply`,
* **masscanned** answers to `TCP SYN` (any port) with `TCP SYN/ACK` on any port,
* **masscanned** answers to `HTTP` requests (any verb) over `TCP/UDP` (any port) with a `HTTP 401` web page.

![demo](doc/img/demo.gif)

**Masscanned** currently supports most common protocols at layers 2-3-4, and a few application
protocols:

* `Eth::ARP::REQ`,
* `Eth::IPv{4,6}::ICMP::ECHO-REQ`,
* `Eth::IPv{4,6}::TCP::SYN` (all ports),
* `Eth::IPv{4,6}::TCP::PSHACK` (all ports),
* `Eth::IPv6::ICMP::ND_NS`.
* `Eth::IPv{4,6}::{TCP,UDP}::HTTP` (all HTTP verbs),
* `Eth::IPv{4,6}::{TCP,UDP}::STUN`,
* `Eth::IPv{4,6}::{TCP,UDP}::SSH` (Server Protocol only).

## Try it locally

1. Build **masscanned**
```
$ cargo build
```
2. Create a new net namespace
```
# ip netns add masscanned
```
3. Create veth between the two namespaces
```
# ip link add vethmasscanned type veth peer veth netns masscanned
# ip link set vethmasscanned up
# ip -n masscanned link set veth up
```
4. Set IP on local veth to have a route for outgoing packets
```
# ip addr add dev vethmasscanned 192.168.0.0/31
```
5. Run **masscanned** in the namespace
```
# ip netns exec masscanned ./target/debug/masscanned --iface veth -v[vv]
```
6. With another terminal, send packets to **masscanned**
```
# arping 192.168.0.1
# ping 192.168.0.1
# nc -n -v 192.168.0.1 80
# nc -n -v -u 192.168.0.1 80
...
```

## Use it

A good use of **masscanned** is to deploy it on a VPS with one or more public IP addresses.

To use the results, the best way is to capture all network traffic on the interface **masscanned** is listening to/responding on.
The pcaps can then be analyzed using [zeek](https://zeek.org/) and the output files can typically be pushed in an instance of **IVRE**.

A documentation on how to deploy an instance of **masscanned** on a VPS is coming (see [Issue #2](https://github.com/ivre/masscanned/issues/2)).

## Protocols

### Layer 2

#### ARP

`masscanned` anwsers to `ARP` requests, for requests that target an `IPv4` address
that is handled by `masscanned` (*i.e.*, an address that is in the 
IP address file given with option `-f`).

The answer contains the first of the following possible `MAC` addresses:

* the `MAC` address specified with `-a` in command line if any,
* the `MAC` address of the interface specified with `-i` in command line if any,
* or the `masscanned` default `MAC` address, *i.e.*, `c0:ff:ee:c0:ff:ee`.

#### Ethernet

`masscanned` answers to `Ethernet` frames, if and only if the following requirements are met:

* the destination address of the frame should be handled by `masscanned`, which means:
    
    * `masscanned` own `MAC` address,
    * the broadcast `MAC` address `ff:ff:ff:ff:ff:ff`,
    * a multicast `MAC` address corresponding to one of the `IPv4` addresses handled by `masscanned` ([RFC 1112](https://datatracker.ietf.org/doc/html/rfc1112)),
    * a multicast `MAC` address corresponding to one of the `IPv6` addresses handled by `masscanned` ;

* `EtherType` field is one of `ARP`, `IPv4` or `IPv6`.

**Note:** even for a non-multicast IP address, `masscanned` will respond to L2 frames addressed to the corresponding multicast `MAC` address.
For instance, if `masscanned` handles `10.11.12.13`, it will answer to frames addressed to `01:00:5e:0b:0c:0d`.

### Layer 3

#### IPv4/IPv6

`masscanned` answers to `IPv4` and `IPv6` packets, only if:

* no `IP` address is specified in a file (*i.e.*, no `-f` option is specified or the file is empty),

**or**

* the destination IP address of the incoming packet is one of the IP addresses handled by `masscanned`.

An additionnal requirement is that the next layer protocol is supported - see below.

#### IPv4

The following L4 protocols are supported for an `IPv4` packet:

* `ICMPv4`
* `UDP`
* `TCP`

If the next layer protocol is not one of them, the packet is dropped.

#### IPv6

The following L4 protocols are supported for an `IPv6` packet:

* `ICMPv6`
* `UDP`
* `TCP`

If the next layer protocol is not one of them, the packet is dropped.

### Layer 3+/4

#### ICMPv4

`masscanned` answers to `ICMPv4` packets if and only if:

* the `ICMP` type of the incoming packet is `EchoRequest` (`8`),
* the `ICMP` code of the incoming packet is `0`.

If these conditions are met, `masscanned` answers with an `ICMP` packet of type `EchoReply` (`0`), 
code `0` and the same payload as the incoming packet, as specified by [RFC 792](https://datatracker.ietf.org/doc/html/rfc792).

#### ICMPv6

`masscanned` answers to `ICMPv6` packets if and only if:

* the `ICMP` type is `NeighborSol` (`135`) **and**:
    * no IP (v4 or v6) was speficied for `masscanned`
    * **or** the target address of the Neighbor Solicitation is one of `masscanned`

*In that case, the answer is a `Neighbor Advertisement` (`136`) packet with `masscanned` `MAC` address*

**or**

*  the `ICMP` type is `EchoRequest` (`128`)

*In that case, the answer is a `EchoReply` (`129`) packet.*

#### TCP

`masscanned` answers to the following `TCP` packets:

* if the received packet has flags `PSH` and `ACK`, `masscanned` checks the **SYNACK-cookie**, and if valid answers at least a `ACK`, or a `PSH-ACK` if
a supported protocol (Layer 5/6/7) has been detected,
* if the received packet has flag `ACK`, it is ignored,
* if the received packet has flag `RST` or `FIN-ACK`, it is ignored,
* if the received packet has flag `SYN`, then `masscanned` answers with a `SYN-ACK` packet, setting a **SYNACK-cookie** in the sequence number.  

#### UDP

`masscanned` answers to an `UDP` packet if and only if the upper-layer protocol
is handled and provides an answer.

### Protocols

#### HTTP

#### STUN

#### SSH

`masscanned` answers to `SSH` `Client: Protocol` messages with the following `Server: Protocol` message:

```
SSH-2.0-1\r\n
```

## Internals

### Tests

#### Unit tests

```
$ cargo test
   Compiling masscanned v0.2.0 (/zdata/workdir/masscanned)
    Finished test [unoptimized + debuginfo] target(s) in 2.34s
     Running target/debug/deps/masscanned-b86211a090e50323

running 36 tests
test client::client_info::tests::test_client_info_eq ... ok
test layer_2::arp::tests::test_arp_reply ... ok
test layer_3::ipv4::tests::test_ipv4_reply ... ok
test layer_3::ipv6::tests::test_ipv6_reply ... ok
test layer_4::icmpv6::tests::test_icmpv6_reply ... ok
test layer_2::tests::test_eth_reply ... ok
test layer_4::icmpv6::tests::test_nd_na_reply ... ok
test layer_4::tcp::tests::test_synack_cookie_ipv4 ... ok
test layer_4::icmpv4::tests::test_icmpv4_reply ... ok
test layer_4::tcp::tests::test_synack_cookie_ipv6 ... ok
test proto::http::test_http_request_field ... ok
test proto::http::test_http_request_no_field ... ok
test proto::http::test_http_request_line ... ok
test proto::http::test_http_verb ... ok
test proto::stun::tests::test_change_request_port ... ok
test proto::stun::tests::test_proto_stun_ipv6 ... ok
test proto::stun::tests::test_proto_stun_ipv4 ... ok
test proto::stun::tests::test_change_request_port_overflow ... ok
test smack::smack::tests::test_anchor_end ... ok
test smack::smack::tests::test_anchor_begin ... ok
test smack::smack::tests::test_multiple_matches ... ok
test smack::smack::tests::test_http_banner ... ok
test smack::smack::tests::test_multiple_matches_wildcard ... ok
test smack::smack::tests::test_proto ... ok
test smack::smack::tests::test_wildcard ... ok
test proto::tests::test_proto_dispatch_ssh ... ok
test proto::tests::test_proto_dispatch_stun ... ok
test synackcookie::tests::test_clientinfo ... ok
test synackcookie::tests::test_ip4_dst ... ok
test synackcookie::tests::test_ip4_src ... ok
test synackcookie::tests::test_ip4 ... ok
test synackcookie::tests::test_ip6 ... ok
test synackcookie::tests::test_key ... ok
test synackcookie::tests::test_tcp_dst ... ok
test synackcookie::tests::test_tcp_src ... ok
test smack::smack::tests::test_pattern ... ok

test result: ok. 36 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
```

#### Functional tests

```
# ./test/test_masscanned.py
tcpdump: listening on tap0, link-type EN10MB (Ethernet), snapshot length 262144 bytes
INFO    test_arp_req......................................OK
INFO    test_arp_req_other_ip.............................OK
INFO    test_ipv4_req.....................................OK
INFO    test_eth_req_other_mac............................OK
INFO    test_ipv4_req_other_ip............................OK
INFO    test_icmpv4_echo_req..............................OK
INFO    test_icmpv6_neighbor_solicitation.................OK
INFO    test_icmpv6_neighbor_solicitation_other_ip........OK
INFO    test_icmpv6_echo_req..............................OK
INFO    test_tcp_syn......................................OK
INFO    test_ipv4_tcp_psh_ack.............................OK
INFO    test_ipv6_tcp_psh_ack.............................OK
INFO    test_ipv4_tcp_http................................OK
INFO    test_ipv6_tcp_http................................OK
INFO    test_ipv4_udp_http................................OK
INFO    test_ipv6_udp_http................................OK
INFO    test_ipv4_tcp_http_ko.............................OK
INFO    test_ipv4_udp_http_ko.............................OK
INFO    test_ipv6_tcp_http_ko.............................OK
INFO    test_ipv6_udp_http_ko.............................OK
INFO    test_ipv4_udp_stun................................OK
INFO    test_ipv6_udp_stun................................OK
INFO    test_ipv4_udp_stun_change_port....................OK
INFO    test_ipv6_udp_stun_change_port....................OK
INFO    test_ipv4_tcp_ssh.................................OK
INFO    test_ipv4_udp_ssh.................................OK
INFO    test_ipv6_tcp_ssh.................................OK
INFO    test_ipv6_udp_ssh.................................OK
tcpdump: pcap_loop: The interface disappeared
604 packets captured
604 packets received by filter
0 packets dropped by kernel
```

### Logging Policy

* `ERR`: any error - will always be displayed.
* `WARN`, `-v`: responses sent by `masscanned`.
* `INFO`, `-vv`: packets not handled, packets ignored.
* `DEBUG`, `-vvv`: all packets received and sent by `masscanned`.

## To Do

* Drop incoming packets if checksum is incorrect
* Fix source address when answering to multicast packets.
